Here’s a quick Nuke tutorial with a useful trick for rendering only the paint strokes that you create from a rotopaint node. This allows you to separate the results of your paint from the background, enabling you to warp and morph and color correct it in order to integrate it with the background.
There’s also a quick sidebar discussion about the ins and outs of linking rotos and transforms to Tracker nodes.
It’s worth mentioning that this technique is not suitable for all situations. There are circumstances where it would actually be more desireable to paint a cleanplate on a single frame and track that in, rather than only using the strokes that generated the cleanplate. This strategy is very useful in many circumstances however, especially when you need to extract only the area affected by your paint.