when viewing a photo in a category as admin you should see the link or ajax button to MAKE ALBUM COVER. You can hit this link to tag the image as the category avatar.
i hate bumping old threads, but i have a question about this exact same thing and i hate starting a new thread for an old topic.
ok, does the thumb HAVE to be in that category? is there no way to set a manual thumb? i've noticed that i can set a manual thumb for photos in the gallery by going into the data folder on the ftp and adding the thumb into the 'thumbnail' folder of the correct gallery. is there not a way to put the thumbnail into a specific folder so that it doesn't have to acutally be in that gallery? the reason i'm saying is because one of my galleries is for pdf files only, and i don't want to have one oddball picture sitting in there just so that i can have the thumbnail for he gallery. any ideas?
i figured it out. you can do exactly what you said...only hide the image after that. it still shows up as the thumbnail for the gallery, but it doesn't show in the gallery itself.