Is there any software on the PC that can flatten crooked photos?

The following are some commonly used softwares for your reference:

1.Adobe Photoshop: As an industry standard image processing software, Photoshop provides various functions and tools to adjust and repair photos. You can use the tilt or rotation function in the transformation tool to adjust the tilt angle of the photo.

2.GIMP: GIMP is a free open source image editing software, similar to Photoshop. It also provides a similar "transform" tool, which can be used to adjust the angle of photos.

3.Lightroom: Lightroom is a professional post-processing software for digital photography. It provides a wealth of adjustment options, including rotation, cropping and perspective correction, which can effectively correct distorted photos.

4. Corel Paint Shop Pro: Paint Shop Pro is another powerful and easy-to-use image editing software. It provides many adjustment tools and filter effects, including rotation, cropping and perspective correction.

These softwares all have different learning curves, so it is suggested to try different softwares first and choose the most comfortable and favorite tool. In addition, before using these software to make adjustments, it is best to back up the original photos to prevent irreversible changes.