Gravatars in Salesforce, using instructions from: http://salesforce.stackexchange.com/a/486

salesforce-gravatars.js

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(function($){function safe_add(x,y){var lsw=(x&65535)+(y&65535),msw=(x>>16)+(y>>16)+(lsw>>16);return msw<<16|lsw&65535}function bit_rol(num,cnt){return num<<cnt|num>>>32-cnt}function md5_cmn(q,a,b,x,s,t){return safe_add(bit_rol(safe_add(safe_add(a,q),safe_add(x,t)),s),b)}function md5_ff(a,b,c,d,x,s,t){return md5_cmn(b&c|~b&d,a,b,x,s,t)}function md5_gg(a,b,c,d,x,s,t){return md5_cmn(b&d|c&~d,a,b,x,s,t)}function md5_hh(a,b,c,d,x,s,t){return md5_cmn(b^c^d,a,b,x,s,t)}function md5_ii(a,b,c,d,x,s,t){return md5_cmn(c^
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<script>
jQuery( document ).ready( function() {
	if( $('.contactTab #con15_ileinner a').length ){
		var email = $('.contactTab #con15_ileinner a').text().trim().toLowerCase();
		var gravatarhash = ( 'http://gravatar.com/avatar/' + $.md5( email ) );
		$('#contactHeaderRow div.headerPhotoContainer img.socialProfilePhoto').attr('src', gravatarhash);
	}
	if( $('.leadTab #lea11_ileinner a').length ){
		var email = $('.leadTab #lea11_ileinner a').text().trim().toLowerCase();
		var gravatarhash = ( 'http://gravatar.com/avatar/' + $.md5( email ) );
		$('#contactHeaderRow div.headerPhotoContainer img.socialProfilePhoto').attr('src', gravatarhash);
	}
});
</script>

Updated with Beau's fork, and removed the comment re: md5 plugin since Salesforce minifies everything.