bypass upload challenge headache

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Okay here is a source code of the php file that controls upload and now my head is fucked, I spent more than 4 hours trying to bypass this one but no solution , anyone has an idea ?

http://code.suck-o.com/42565" onclick="window.open(this.href);return false;

[ayu]

The assignment is to bypass the extension check and upload a php file or?

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from the code its not just the extension because every file u can upload will become called "jp" or "jpeg etc because of the strrpos funtions and substr() and yup the goal is to bypass all that to upload a shell