DIY Pattern Generators or Custom Generator Companies

I'm sure you've seen the laser pointers at the gas station for $5 with a bunch of caps with different patterns. I have a nice green pointer and I'd like to put a custom picture on it. I haven't looked into these much, but I looked under a microscope to see if I could even detect the pattern on those cheap caps but it was a no-go.

Anyone know how to either make them or get one custom made?