jit.repos maybe? a two dimensional matrix repositions the pixels. theoretically you could animate this matrix.
Jitter Tutorial 39 shows the power of this approach.
another (actually performative much faster) posibility would be to play around opengl and uv-mapping. however this is more complicated because you would be forced to create your own 3d plane and the texturemapping coordinates.
the patch I posted with this question of mine (http://cycling74.com/forums/topic.php?id=24438) plays with jit.gl.sketch, and the big messagebox shows how to create your own plane together with the uv-mapping coordinates. with the help of those you can decide which part of the image should be mapped where on the plane object. this way a kind of morphing could be made possible, but still leaves open the question on what you actually want to achieve...
This is not a particularly easy effect to create from scratch. Like any other popular graphics effect, the technology behind "morphing" is well documented if you look in the right places. It is mainly a matter of digging through white papers and plucking out the relevant concepts. You will probably want to spend some time looking at OpenGL, as t0gg1e4u suggests.
Thanks for these suggestions; really we're not sure what we want to do, it's for a student of mine who is doing a musical project using an interactive whiteboard, and we needed some... interesting slowly changing images? I think what we're going to go with at the moment are some video renders using Norrkross MorphX http://www.norrkross.com/software/morphx/ - that was the kind of 'morphing' I was looking to do - plus some live bitwise xor crossfades from tutorial 9. I'll look into jit.repos as well.