How did i get the zombie face profile pic to the left here? Are the different default profile pics based on what year your character was created? How do you change it if you want to? I actually like the zombie head cause no one else seems to have it but i dont know how i got it.
That particular picture comes from the Ghoulish Mask, which has a right-click option to take an avatar photo. You can read more about that item on the Wiki: https://runescape.wiki/w/Ghoulish_mask
However, most items don't work like that - instead, you visit the Photobooth which is located near the Makeover Mage (south-west of Falador) wearing whatever you would like to show in your picture, and can take and update your forum avatar through that.