Are you going to use a server side code or the unreliable mailto? Either way you will need to be able to "write" the content in HTML, otherwise you will only be sending code.
<script type="text/javascript">
function sendmail(){
px=document.getElementById('dapic');
//px=document.getElementById('dapic').src;
destination=document.getElementById('dadestiny').value;
window.open('mailto:'+destination+'?Subject=PICTURE!!&body='+px);
}
</script>
<img id="dapic" src="http://photos-e.ak.fbcdn.net/hphotos-ak-snc3/hs124.snc3/17174_236072693_707693_3779876_6145813_n.jpg">
<input id="dadestiny" >
<input type="button" value="send mail" onclick="sendmail();">