How to identify tampered images with PS software

How to use PS software to identify tampered images

With the popularization of digital cameras and computers, the era of national photography has arrived. But what about the photography that followed? Fake? Events are also endless. The following is how I searched to identify tampered pictures with PS software, hoping to help everyone! For more information, please continue to pay attention to our fresh graduates training network!

Photography is divided into pre-shooting and post-image production. In the era of film photography, the complex darkroom technology is only mastered by a few professionals. After entering the era of digital photography, with the rapid development of computer image technology, all kinds of software can be used to process digital images, among which AdobePhotoshop (PS) image processing software is the most widely used, the most powerful and easy to operate. The image formed by computer image processing is almost indistinguishable from the real natural image visually. For modifying the image, it is mainly based on? PS software? In the main cases, the methods, characteristics and tests of adding, deleting and tampering images by using computer image processing technology are expounded, and how to effectively distinguish and identify real natural images from later modified images is determined.

1. Methods of adding, deleting and tampering with images by PS software

The compositing function of PS software plays an important role in image processing. Composition is not a simple piece of work. It needs to use all kinds of materials to get new materials through organization, processing, modification and fusion. Design? Works, in order to achieve the ideal effect, so you need a high artistic accomplishment and PS operation ability. In recent years, there are many ways to modify images by computer image processing technology.

1. Use PS software to add content to the picture.

Adding a picture is to take it out of a picture (that is? Interrupter? ) part, and then add it to another picture to generate a new picture, that is, synthesize the picture with PS. First, select a suitable material, then use the selection area to select the parts that need to be replaced, paste them on the material map, then use the mask to control the area, and finally modify the overall color matching and details.

2. Delete and modify the content in the middle of the picture with PS software.

Without affecting the integrity of the picture, there are many ways to delete the parts you don't want in the picture, mainly poking tools and establishing the selection area. If the scene to be mended is surrounded by white or monochrome, it can be mended with a solid color brush.

3. Use PS software to transform and blur the image.

The method to modify the image is to use PS software to deform and blur the image. The methods that can be used to deform images in PS software include: free transformation, liquefaction filter, distortion filter and so on. This command can transform an image into a special shape.

Second, use PS software to add, delete and tamper with image features.

Repairing the changed image is one of the common means to use PS image processing technology. This paper mainly uses various editing functions of PS image processing software, such as moving, deleting, cutting and pasting, rotating, local enlargement and modification, to process images and make new images.

Forging a photo refers to deliberately making a photo that doesn't actually exist, and its outstanding performance is that the photo is not true. Fake photos usually show a new content by editing, copying and synthesizing different parts of real photos. The behavior of changing other parts is that the photo already exists objectively, which is formed by the producer modifying and editing the existing photo according to his own needs. Alteration is generally divided into three types.

(1) Additional changes. Just add something to the photo screen.

(2) Alteration of deletion. Is to cut or delete something on the photo screen.

(3) Changes combined with additions and deletions. In the process of actually checking unreal photos, it is often encountered that there are both additions and deletions in the photos, as well as the combination of additions and deletions, which makes the inspection more difficult.

Third, the identification method of PS software adding, deleting and tampering with pictures

No matter how hard the altered image is made, after careful observation, the modified photo will always leave clues. For the inspection of such suspicious images, we should adopt various methods and carry out inspection from various aspects and levels. In many cases, it is difficult for people to find defects with the naked eye. With the help of PS software, the authenticity of digital images can be comprehensively judged.

1. View Exif of digital photos with PS software? Metadata?

Exif of digital photos? Metadata? Is an image file format, which has two versions: V2. 1 and V2.2 It adds all kinds of shooting information collected by digital cameras in the shooting process to the Jpeg file header, such as camera data (such as camera manufacturer and model, etc. ), shooting parameters (such as shutter speed, focal length, etc. ) and the thumbnail information of the photo (depending on the camera), the size is 2 ~ 6 KB (depending on the camera), and the tag is encoded and stored in the Jpeg image file. View with PS full version, first open the digital photo, pass? File introduction? In the options? Exif？ View, there are more than 30 image descriptions (such as camera model, shooting time, etc. ), user comments (such as Exif color space, etc. ) and related sound files (such as file source, scene type and Exif standard).

2. Enlarge photos with PS software.

Based on the scientific theories of scene imaging, illumination and color filtering, the brightness density, contrast, hue and gray value of the scene in the suspected forged area in the image are observed and compared, and whether there is any contradiction with the imaging principle in the picture is analyzed, so as to judge whether there are any alteration marks in the photo. In a natural image, the probability that two or more spatially coherent regions (including color, shape, texture, etc.) exactly match. ) is very small, so the key to successfully identify the copied and tampered areas in the image is to determine the size and characteristics of the image block. In photo inspection, PS is used to enlarge the image, and then by observing the edge of the object in the photo, whether the depth of field of the photo conforms to the law of lens imaging, the difference of image noise, the continuity of color and so on. , you can judge whether the photos were taken under the same lighting conditions, so as to judge the authenticity of the photos.

(1) Check the edge of the subject (details of the edge such as hair, etc. ) The photo is ambiguous. Most fake photos often put good subjects in an ideal environment to increase the news and beauty of the picture. The edge of an image can be defined as the discontinuity of local features of the image, which is manifested by the sudden change of image gray level, texture structure and color, which makes the edges of these subjects often not smooth. After high magnification, you can find that there are many vague traces in these places.

(2) Check whether the depth of field of the photo conforms to the law of lens imaging. Whether using wide-angle lens or large telescope, the depth of field is regular. However, altered photos often fail to conform to these laws.

(3) Check the noise of the image. Digital camera noise is visible error information caused by CCD/CMOS or digital signal system. Visible noise in digital images is usually affected by temperature and ISO sensitivity. The higher these two values, the worse the effect. Using the different background noise of different digital cameras and the different noise of photos taken under different ISO sensitivities, the regional statistical comparison method of image noise after high magnification can test the originality of digital images. (4) Check the continuity of image color. Color is considered as the most valuable potential feature of an image. For the real image with complex background, the color features have relatively good continuity, the color transition is soft, and the RGB values of colors between adjacent pixels are different. The color of the added image suddenly changes between the edge and the background, or the pixels are similar, and the RGB values of the colors between adjacent pixels are the same.

(5) Check the rationality of actual changes. The clarity of digital images is related to the position of the focusing plane and the depth of field when shooting. For static objects, when the clarity of things outside the depth of field in the image exceeds that of the scene within the depth of field, it should be an altered image after addition, replacement or synthesis. However, when there are moving objects, the irrationality of the change of reality and reality caused by improper operation should be ruled out. The definition of a still object in an image should be higher than that of a moving object, but the definition of a moving object can be higher than that of a still object if the following methods are adopted.

3. Measuring comparison method with PS software

Using the measuring tools in PS software, the similarities and differences between the shooting angles of the suspicious part of the photo and the background, the direction of the shadow, the direction of the light source and the perspective relationship are determined, so as to determine the authenticity of the picture.

(1) Measure whether the shooting angle of the subject in the photo is the same as that of the surrounding environment. what's up Contradiction? Different shooting angles will have different visual effects. If there is a contradiction between the subject and the surrounding environment in the shooting angle, you can see that this is a photo taken from two different shooting angles? New pictures? .

(2) Measure whether the shadow direction of the object in the photo is uniform. Fake photos often put together photos taken at different times, places and environments. Different lights will appear in many ways, so different shadows will appear. Through the shadows, we can also find flaws in fake news photos. The added image and the shadow of the background will be obviously different in intensity and length.

(3) Measure whether the light source direction in the photo is uniform. The light in the picture should be uniform, not contradictory. Consistency of light angle In the same digital image, the direction and position of the main light source are determined, and the light and shade changes of the concave and convex parts of the subject should be consistent with the length and direction of the shadow. When a scene in an image shows unexplained light and dark changes or shadows, it can be judged that the image may be tampered with. The transition between light and shade in digital images is gradual and natural. But when synthesizing a new photo, people or things in different photos will inevitably take different photos because of different shooting conditions. Therefore, when stitching two pictures, it is difficult for the light at the seam to have a natural transition.

(4) Measure whether the proportional relationship of imaging perspective in photos is consistent. According to the perspective principle, in the test to determine the authenticity of the image, we can measure and analyze whether there is a phenomenon that violates the perspective law in the image by comparing the size perspective, direction perspective, tone perspective and the proportional relationship of the object's sound quality. If the rules of perspective imaging are violated, for example, the parallel straight lines of non-parallel images do not disappear to a point, the proportions from near to large and from far to small do not conform to the perspective effect, and the line segments in different directions do not disappear to the sky or place when they are not parallel images, then there must be an added part in the photo. At this time, it is necessary to carefully observe and analyze the additions and deletions in the photos.

4. Use PS software to change the tone of the image.

Tone refers to the black and white tendency of photos. Modification marks in high-profile or low-profile photos, as well as those in highlights or dark parts, are difficult to find, and modification marks may be exposed after trying to change the tone of photos. Adjust the image tone in the opposite direction with PS image processing software, that is, high-profile photos become brighter, low-profile photos become darker, and middle-tone photos become brighter and darker respectively. Then enlarge the photo to 100% to observe the bright or dark parts, and there will be some places such as addition and deletion, uncoordinated background areas, poor image quality, irregular imaging and so on.

This paper briefly introduces the methods and characteristics of image modification, and discusses the simple methods of identifying forged images. With the continuous development of modern digital technology, more advanced image forgery means will inevitably appear, which poses a higher challenge to the identification of digital images. Because image forensics is a completely open research field, it has been paid full attention by scientific research institutions, judicial organs and the press. It is believed that with the gradual development of image forensics technology, the theoretical research on image authenticity will continue to deepen and the digital image identification system will be improved and standardized.

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