There is a limit on the total size of file attachments (75 mb) and it looks like we hit that recently. This limit is arbitrary and can be changed, but it would probably be better not to use the forum database as default photo storage as this will over time cause it to balloon in size.
I will probably expand the limit for attachments pretty soon. In the meantime, please post photos to the file hosting service of your choice. This is the one I usually use. It's very clean and they allow you to upload without registration. https://postimages.org/
At some point I would like to set up some sort of file storage for us to use for important files.