A scanner is a real help. I tweek my decal files in Adobe Illustrator.
I have an inkjet printer and it does help to give it a couple of days to dry.
Try to get a setting where if you are scanning decal sheets, eliminate or minimize the blue background of the paper.
I realize that wasn't the question, but tips help.
1. Create art file in drawing programm, by scanning a decal sheet, by using a photograph or etc.
2. Print on plain paper enough times to get the size, resolution, color as good as possible.
3. Print once more on plain paper fed through the manual feeder if that's how your machine works, or from paper tray. Mark that page so you can mimic orientation and which side is up.
4. Take that last print and cut a piece of decal paper large enough to cover the image you want to make into a decal and tape it down along the leading edge, outside the image area.
5. Print on that. The idea is to not have to use a whole decal sheet because it doesn't really work to print repeatedly on the same paper -and saves decal film.
6. I'll let them dry for a couple of days.
7. Spray with a very thin coat of Testors Decal Bonder. One coat should work, you will find out.
One parameter of many- my machine prints better when it's cold.
Bill