on a 1:1 basis you can see if a file itself is identical straight through the windows command line:
fc <file1> <file2> /b
Of course that doesn't account for 'identical' files saved in different formats. If you do a pixel-by-pixel comparision of an image file, also keep in mind that different formats may introduce differences, e.g. if you have a .PNG and save it as a .JPEG, you'll introduce differences thanks to the lossy compression algorithms uses that subtly change the data and thereby certain pixels in the process.
fc <file1> <file2> /b
Of course that doesn't account for 'identical' files saved in different formats. If you do a pixel-by-pixel comparision of an image file, also keep in mind that different formats may introduce differences, e.g. if you have a .PNG and save it as a .JPEG, you'll introduce differences thanks to the lossy compression algorithms uses that subtly change the data and thereby certain pixels in the process.