Detect if your visitors have a gmail account

Interesting technique learned in hacks.mozilla.org how can know if your visitor have a gmail account or not:
You have a gmail account active
You don't have a gmail account active
Code here:

<span id="youhavegmail" style="color: #274e13; display:none;"><b>You have a gmail account active</b></span> 
<span id="youdontgmail" style="color: #660000; display:none;"><b>You don't have a gmail account active</b></span> 
<img onerror="document.getElementById('youdontgmail').style.display = '';" onload="document.getElementById('youhavegmail').style.display = '';" src="https://mail.google.com/mail/photos/static/AD34hIjNph9m60xryTIHSxJ1GeKUOWjfmI08q5-3fuhEJZ43GPlXoBg5cScOXtNEwH18hxyK-W3ZYFU3Lv1md9mh3d2jePsyvg91h-V65DSyFfHelnN_yPc" style="display: none;" />

More info at: http://hacks.mozilla.org/2011/02/an-interesting-way-to-determine-if-you-are-logged-into-social-web-sites/

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Posted at BinaryCell