To import an photo and place it in the background do: Go to the File Browser and find the photo. Click on the Import button,
To export the clip: Go up to File, Export. Set Export to "QuickTime Movie". Click on the OPtions button and set the codac (Compressor) that you like. I prefer to export it out as an Animation clip. And then compress in compressor.
Hope this is the answer you are looking for. Best of luck.
I put together a really quick example of a video looping 4 times.
In a nutshell I created a particle and then keyframed it's life so it would go off the screen. I then layered the particle so it would appear as if it is looping if you cut part of it out. I think it is easier for me to give you the project file and let you take a look. Please take a look at the attached project file. 418_particleloop.motn.zip At 3:04 and around 9:17 the particles are the same. I just looped that 4 times in FCP and this is the results. Hope this helps.