I read somewhere that bluejays have unique facial markings and they may use them to tell each other apart. I have uploaded 24 pictures of bluejays from the feeder cam into
this Imgur album.
I know we have at least 2 bluejays in the yard, as I witnessed both of them as they were building a nest. While I *think* I've seen them both at the same time near the feeders, I do not know if they both come to the windowsill, so I may have 24 pictures of the same bird.
Anyway, if you feel like staring at 24 pictures of birds to see if you can tell them apart, have at it. I haven't been able to spot any differences yet.
(If it helps, going across from left to right, then down, I know that pictures 2-4 are the same bird, as are pictures 5-10, 11-12, 13-15, 17-19, 20-22, 23-24, as they each came from the same batch of 5-6 shots.)