The basic technique I use to build these things is described here:

http://www.krazydad.com/visco/howitworks.php

(oh look at that - I need to update the CSS on that page…)

And there’s also a faq here:

http://www.coverpop.com/faq/

After reading that, you will probably have a few questions about the
flash interface. Basically, there are no buttons, and a single movieclip
is used to display the captions. I track the mouse movement over the stage,
and when I decide it’s time to pop up an image, I download the image, and
overlay it on top of the background, animating it to match-move with the original
placement in the mosaic.