Dynamic display images

[AH]

I have an image area in the top.htm and want to display different
images when go to different HTML pages. Maybe even change images every
n sconds. Does HTML support if-then-else or case statements? What is
the syntax?

If not, can someone provide me a method to "dynamic" display images
based on the current HTML page or time? Please provide the sample codes
if possible.

Thanks,
AH