Shameless plug, eh? I don't think your product really showcases how most Facebook photos are poor quality since you pull news images as well. I know most of the pictures in my feed are some that I don't give two cares about.
This is HackerNews, of course the plug comes first :)
In answer to your question though, yes, quality is not a guarantee. Luckily Facebook has its own built in ranking system - are your friends commenting on the picture? If so, it will probably be worth viewing regardless of image quality
Cool concept, by the way!