I have noticed a fair amount of users looking for specific images, and asking for help to find them. While I Understand you may be having trouble finding it, I would like to say that searching and using tags may help you find it even quicker than asking the forum!
Remember, tags with spaces use underscores (_) ex: "bugs_bunny" not "bugs bunny", and posts can be sorted by your chosen criteria. For example, want to find an image which you remember had a high score, simply add "order:score" to your search.
So if you have trouble finding a specific image, remember to search with the appropriate tags and tools available! Although if you do have a problem finding the image after searching around, do feel free to ask in the forum! Just bear in mind it may take a while for someone to respond.
Oh, and not ALL images are on here, in this case you might want to check another site such as rule 34 or furaffinity.
Anyway, good luck searching, and I hope I helped.
Update: here is a full list of the searching criteria in case you forget or are new here https://e621.net/help/cheatsheet
Updated by Knotty Curls