Well I've had this problem for a while and I'd really like to know a good way to fix it.
I don't remember ever having this problem when I first started making decals, but it's started to really get on my nervs. I don't notice this with any of the defaults or a lot of other decals. White lines always appear on whatever I make, almost always if it's a black outline of some sort.
I really wanted to fix this problem when Siba was making a box model for me and I made some textures for him. It is a cardboard box so I thouht some "THIS SIDE UP" and "FRAGILE" type things on it would be fun. But the "THIS SIDE UP" one got this lovely white line problem on it. I'm sure the Fragile one does too but it isn't noticeable at all because it has an actual white outline to start with.
I also noticed it completely ruined 2 of my face decals that I really kinda loved before they did that white line thing.
click for full:

I use Adobe Photoshop to make my stuff. I've never tinkered with the anti aliasing options or anything. I'd really love to know how to get rid of this crap, or if there's another program I can use that won't give me this problem (that is free)
Sorry if this is in the wrong section, I've never used the Modification Discussion boards before, but I was pretty sure this was the place to go. Thank you for any help you can give me.