I can't for the life of me figure out how to import a single picture and be able to move it around. I don't think that it should be so hard, but I can't find any way to. Maybe it's because I am so used to Cinema 4D and After Effects? The interface isn't too easy in this program.
There's no way to animate the position of a background image, but you can import a picture as an emitter's shape, set the emitter to Single Particle, and then increase the Visibility all the way up. The walking mouse emitter is an example of this, just with an animated image rather than a single picture.
The only problem with this method is that since particle shapes have to be to the power of 16 pixels (256x512, 128x128), your image will get squished if it's not that size.
Using a program like photoshop, You can always make the image fit into one of those dimensions and either leave black on the edges or transparency as needed. I've not tried that, but it should work, allowing you to have you image at full size without getting squished.