I'm affraid thats not possible. You can search in the picture gallery and make selections that way. But you cannot sort them.
Technically speaking, it could be possible to do that. We have to add a custom field with the blocks for all aircraft. But practically, its almost impossible to retrofit all those pictures we have with that data. You have to remember that we're close to 13,000 pictures in our gallery. It would simply take too much time to do all that work.
However, you can definately search on blocks. We did add the block of every F-16 picture that we have. So if you type 'block 15' in the search engine, you should get all the pictures of the block 15 airframes.