Hi Edvard,
This may not directly address your question, but you may wish to check out the software available from...
Reallusion.com
They are described as....
"
Reallusion is a leader in the development of 3D cinematic animation and 2D cartoon softwares for consumers, students and professionals."
I don't know their entire product line, but I do own their product CrazyTalk, which is just fantastic. Here's an example of what can be done with it, and keep in mind I am a very novice user using the most basic version of CrazyTalk.
BTW, if the above video looks like something you'd want to do, you may be able to get CrazyTalk7 for free, given that it is an old now out of date version. They gave it to me for free.
I've been diving in to the 3D realm in recent months, and if you don't already know, be aware that much of it is very complex. However, 2D cartoons should be much simpler.
Another software which may possibly be of interest is
Morph Age. This allows you to animate a photograph. I'm not sure it's the ideal tool for cartoons, but it may merit your inspection nonetheless. Excellent app, and great company.
Good luck with your projects!
http://www.reallusion.com/