Perhaps you should consider deleting images from all posts from a year or so back that have long been seen by anyone interested. Wouldn't that make room for newer more topical posts? (I get the same error message constantly that "the board has reached its quota.")
Here's a second vote for PhotoBucket. There are many free alternatives for us. Just create an account at one of the other services, load the photos there, copy the link to the photo, and post the link here.