At the same time, photos taken with mobile phones and digital cameras were uploaded. All names have a string of numbers. IMG, SDC, PIC. What is this, a pixel?

IMG, these are all English abbreviations, like the number after the image, which is usually a common number (including date and other information). If you enter file management on your mobile phone, check the details of the picture file on your computer, right-click the file and select the last attribute, and then select Advanced to see it.