Oh, there's a new "Fade Picture" button in the Postaility Knights version. Yes, the XP. I didn't know there was a Postaility Knights version for anything else but XP. Sorry for wasting your time guys.
You weren't wasting anyone's time. The only Postality Knights version IS for XP. So, by saying your problem was for the Postality Knights version, without mentioning anything else, gave it away that it was XP, so don't worry. As for your problem, I figured someone would have gotten to this now.... I'll try to help.
Use a series of Show Picture commands, making the first one almost completely transparent, or opaque, or whatever the term is they use. (I don't have access to XP at the moment.) Then, make it a wait command, followed by another show picture command of the same picture, only slightly less transparent, or opaque, or whatever, and keep going until it's fully visible. It sounds like it's would be really slow watching it in the game, but if you do it right, I'm sure it'll turn out the way you want it to.
There may be an easier way to do this, but without access to XP, I can't tell you exactly how right now. I hope this helps you, and maybe someone can elaborate on what I've said already.