Beta

You have to upload the image on a website, for example http://imgur.com. You'll get a link like this: http://i.imgur.com/qNbtHF9.jpg, once you've succesfully uploaded the image.

Save the link, and go back to editting your signature, now put the link in the [img][/img] tags like so: [img]http://i.imgur.com/qNbtHF9.jpg[/img].
You can also choose to align the the image center or right using one of these tags: [center][/center] or [right][/right].

[center][img]http://i.imgur.com/qNbtHF9.jpg[/img][/center] will result in:

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