I'm using timthumb (latest version) on ubuntu. I'm also having this issue with other scripts, and I've written my own code, same problem every time as long as I'm using GD.
When resizing this:
I get this:
(The ?h=150 reroutes the request through timthumb)
There's a speckled background, and the border of the text is gray. The original above looks nothing like that.