[noodle]

i'm not sure if i understand completely.

if the functionality is a simple toggle, like, click to zoom in, click again to zoom back out, then use a CSS sprite (or something similar) to toggle the icon between a zoom icon with a plus and zoom icon with a minus (so that the image will remain mostly the same and therefore not confusing).

if its something else, either do something more complex to toggle the icon between a variety of icons, all of which being similar. if you're looking for just a single icon, perhaps a simple magnifying glass without any other decoration.

[jacobbijani]

Yeah, you need to either explain the actual functionality you expect to have behind the button or figure that out first. You need to figure out if zooming in and back out again is actually possible with the same element before figuring out how to iconify it.

And if you go for just a toggle, then I agree your best bet is to simply toggle the button along with the state change.