There is only a certain amount of storage available for each member to upload pictures to the site. You have a few options.
Go to userCP, then under networking in the lefthand column click on pictures and albums. You can then delete older pics.
You can upload pictures to your profile album or to a photo sharing site (like photobucket) then link the URL to your posts.
Or you can become a supporting member which allows more photo storage among other things.
Click on the supporter badge under my profile pic and it will take you there.