Okay, for some reason I've been struggling with this excessively the last few days. I've been trying to edit one of Valve's skyboxes, but the problem is that I just can't get the parts to be seamless. I tried getting every part of the skybox in the same picture and editing them as a whole, and then I cut that picture into parts - but there were still seams in the places where the picture ended. I've seen a lot of successful attempts at modding Valve's skyboxes around here - what's the trick? I read [ame=http://forums.tf2maps.net/showthread.php?t=5268]this[/ame] tutorial, but it doesn't really explain how to get the pictures to be seamless.