Then in your HTML source, simply use <img src="foo.rand/"> to pick one of those images.
For example
foo.rand
|
|----- a
| |---- index.html
|
|----- b
| |---- index.html
|
|----- c
|---- index.html
Then in your HTML, use <a href="foo.rand/">. This will
cause the client to be redirected to one of menu pages under a,b or c.