Buttons can be defined by:

<p>Please type the mail to send to Bob Hopgood:
<input name="MyMessage" type="text" />
<br />then mail by pressing:
<input type="image" name="Pretty" src="frah.gif" /></p>

This would appear something like:

Please type the mail to send to Bob Hopgood:
then mail by pressing:

What gets sent depends on where the user has hit on the image. Something like: ..&Pretty.x=73&Pretty.y=122. It is possible to associate a usemap attribute to the input element so that different responses could be made dependent on the input values provided.