AllSync & AllDup

I am searching my NAS for exact duplicate photos. Right now, I am using a MD5 (128-bit) comparison search and having it stop when it finds 1000 duplicates (otherwise, it crashes).

Since this takes so long, is there a way I could do a faster initial search to find files that are similar, and then use the MD5 search on this subset?

No, thats not possible.

btw: you can get a faster search result by comparing only the file size but at the end you have to make sure yourself that the files in the search result are real duplicates or not...