I always see people requesting an "insert picture" block. The reasons I'm going to list may be part of the reason why pictures aren't allowed. Just to clarify, this does not qualify on the forum due to the fact that people post pictures for other Hopscotchers to help and see what they should do with their code.
One reason is that some Hopscotchers may not be responsible enough and publish pictures of themselves and other people. That would go against that Hopscotch rule that states that no personal information is tolerated.
Next, Hopscotchers may publish very violent pictures of something. If anyone is ever caught even chatting about that, other users would report them the minute they are posted. Hopscotch is meant to be a nice learning environment and a fun place.
I think that Hopscotch should pick a set of pictures for users to use instead of users choosing from their photo library. That way Hopscotch can still have pictures, but not risking users putting out their personal information and Hopscotchers being mean.