I've been a Flickr user for years and love the service, but if I could be the Flickr product manager for a day, I'd fix this:
I can't favorite my own photos. And you can't favorite your own photos. There is no technical reason for this. Flickr has simply decided that a user cannot favorite their own pictures, and that is that.
"Oh, silly user -- you can just make a set and put your favorite pictures in that!" No. It's not the same thing. When other people view my favorite pictures under my profile, I want them to see all of my favorite pictures on Flickr, even if some of them happen to be my own pictures. No, I don't want to futz around with photo set management to corral my own pictures into a "Favorites" set. I want to click that little star button and mark it as a favorite.
Another problem with the "just use a set" solution is that Flickr doesn't let me put other people's photos into a set. So that won't let me combine favorites from my photos and from others into a common place either.