It's not a storage space shortage, it's a bandwidth inconvenience. Furthermore, I'd guess there's only one to three dozen duplicates. The current checksum DOES catch 99% of duplicates, but if the pictures are actually different, it allows it. To do other checking would be too CPU intensive and not much more accurate. (eg, giving each picture a lower resolution thumbnail, and comparing it to every other thumbnail.)
This version appears to be of slightly higher quality than the other. Noticable in the hair. This one is also almost twice the size of the othe rone. So if you must delete one, I'd choose the "original"
