capturing images
It depends on how the image is stored. Phelan is correct that flash is a very common source of flashing images and you would only be able to capture the whole animation. There are many other possibilities including animated GIFs, java, vbscript, javascript, shockwave or other plugins, even server-side scripting languages (.asp, .php, etc.). The only way to tell is to look at the source (select "View Page Source" or something like that from your browsers "View" menu). You then may have to load subsidiary pages (by selecting them from the source). With most of these scripts you will not be able to see the actual images but with some (e.g. javascript) you might.