Bitmap based paintbrushes? how to?

Hello, i downloaded Synfig hoping to be able to replace very old creature house expression + livingcels to create animated backgrounds for my animations.
I use a custom technique, usually animating characters in 3d, an making backgrounds using vectorial strokes based on bitmap rendered images…
Here are some still images examples:!/album.php?aid=23233&id=120996867915294
so, what i would need, is :
to import a png bitmap
to use them as a custom vectorial brush

i would also appreciate anyone pointing me to any other modern animation software to do it :slight_smile:

Check if this is the usage you’re looking for: