efficient way to compare 2 images?

[SMcNeill]

If the images are in a file, just open each into a variable with BINARY.

If the variables are equal, the images are the same....

Pete

This may not work for a variety of reasons.   Different formats of the same image.  One was saved compressed, the other wasn't.  One has additional file attributes attached to it, that the other doesn't.  You'd want to load the files into memory and compare the contents of the image once they're loaded.  After all, you want to know if the IMAGES are identical; not the files which contain them.