[Russell Sobie]

Depending on the texture application you are using (Photoshop, GIMP, Paint.net, whatever) you should be able to look at "Channels" and you are looking for an "Alpha Channel". This channel is typically used as a sort of translucency mask for everything else in the image. It is super confusing to mess with... especially since now adays you can use PNGs in many applications and games where you simply do the transparency right in the texture information rather than having an alpha dictate it.

Typically what I do for things like glass numbers (like on the Audi TT Cup) is just make the image full white, and then do all the editing in the alpha channel. That way you don't have to match anything up... you only edit in one place.

Here's the first tutorial I found that may be relevant to give you the basics: https://www.youtube.com/watch?v=FJeb1XjBKUw

If that doesn't help, I can give you a more concrete tutorial here later on this week.