If you want to make an image into a link, you have to put url tags around whatever it is that you're trying to turn into a link.

Here's what you'll need: [url=http://somesite.com/][img]http://www.someimagehost.com/image.png[/img][/url]

For example, using this:
[url=http://lapsus.on.toribash.com][img]http://lapsus.on.toribash.com/images/22009.png[/img][/url]

Will get you this:


For images in your signature, assuming that you have toribash prime, you'd use something this instead:
[url=http://www.example.com][sigpic][/sigpic][/url]