Ok, I'm definitely making forward progress on this. I've md5'd all of my images into a list, and have sorted.
Now I'm trying to figure out how the -k operation works, or rather what it's function is. If I used sort -u -k1,32
would sort use only the first 32 characters of each line to determine uniqueness?
Edit: Ok, I think I figured it out. -kx,y ... x is the field number (as separated by spaces), y is the character position within the field. Right?
P.S. It only took my computer about 1 minute to md5 all 2.3G of images.