It is a perk for frequent users of the site. You must be premium or have at least one star for this option.
In one of the Entertainment forums, you will notice the underlined links seen below, at the top of the forum.
To add yours, click on photo album and follow the instructions. Do the same thing for your pet by clicking on pets.
To change yours, go to the photo album where you posted the graphic. Click on your ID in the link at the top of the page. You may then delete or edit your pictures. To see which album a particular picture is from, you can "hover" your mouse over it, and it will show you the link.