To HumpherBackside's request I offer an explanation
Prelude: I don't have and maintain list of many image hostings with rules how to handle each, it would've been too much work. Instead I wrote "smart" code that tries to handle any image hosting.
About "search for original filename":
Let's say we have thumbnail img yt/upload/small/2016/01/17/569b78795278b.jpg
If I replace 'small' with 'big' I'll get link to full-size image, and I wouldn't need to visit actual hosting page (img yt/img-569b7879527dd.html), It speeds up whole process, a lot.
But from those links I can only know that image name is 569b78795278b.jpg
If you turn on "search for original filenames" program will be forced to visit hosting page and look for name, which is _DSC0001.jpg
search for original filename
ON - higher chance of getting original name, slower downloading process
OFF - lesser chance of finding original name, faster downloading
About prefixes: (001 -)
I always turn them on, here is why: image hostings that 100% do not have original names will totally mess order
If you would like to rename multiple files, e.g. remove first 5 symbols, there are free tools to automate it (https://renamer.com/)
google something like "mac os(linux or w/e) batch rename