If your JPEG is more seriously damaged then the image might be shifted to the left or right from the point of the error. The program will make an intelligent guess at the best colours and display the results immediately. If your image uses the wrong palette from a certain point, or is just entirely black, then all you need to do is move the square to the first block where the error begins, and click 'Fix colors'.
Your mouse cursor has a small square attached to it which represents a JPEG 'Minimum Coded Unit'. Point JPEG Repair Shop at the file and it should load and display, if only partially. That's way too tedious for us, plus it's a bad idea to work with the originals anyway (you don't want to risk corrupting them further), so a better idea is to create a 'Corrupt' folder somewhere and copy your problem image(s) there.
Instead you must point JPEG Repair Shop at the image folder, then manually click 'Next' to step through each picture until you find what you need. You can't drag and drop your target file onto the program. The file selection process is a little bizarre. If you can't open an image at all then it probably won't help, but if you see part of an image, then the rest is black, or the colours change, or a part of the image is shifted to the left or right then there's a chance of success. JPEG Repair Shop is a free portable tool which can repair some types of JPG file corruption.
