Oh wow I'd never seen that post before justjennifer, thank you so much for showing me. I'll bear that in mind for new posts.
However, I only very recently changed most of my posts to Gallery format (without adding all the pictures again through the 'Create Gallery' option). Prior to that I mostly had the 'Standard' style with 1 or 2 in Gallery style and the images in both were interactive, that is to say they opened in a new page with the option to show the full size image. The gallery carousel also worked. Then, and I can't remember when exactly, they just stopped and I never did anything about it, I just assumed it was something to do with WordPress and would sort itself out or it wasn't an available option anymore. Following that I changed then all to Gallery style as I preferred the changes that made to how the posts are displayed in the Reader and on my front page. I finally asked about it here because I realized I could click on images in other people's blogs and they still open/enlarge.
I've just changed the two most recent posts back to Standard format and the images still aren't clickable, so I'm not sure what to do? I've looked through all the settings and can't see any options that I might need to change.