I'm not sure I'm understanding correctly because you mention both text and image but I'm going to give it a shot. If the "image of a button" is the image you are using for a button, or a copy of the image you are using for a button you could blink it by making it an animated gif (which won't quite depress like a button but may look like it if you shade one edge.)
You could make it a mouseover or hover button so it would blink off (or on) when the cursor is over it.
You could also take the easy way and stick the button graphic in a tight table with absolute (as opposed to relative) sizing as the table background image. Then center blinking text over it. (Right click, font properties, special properties, blink) I believe blinking text only works in one browser. I forget which one.
Hope I didn't answer an entirely different question. :/
Good luck,
bunni@bunni.com