How can I change an URL in html output?

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PHP

RSS

I've got a page using simplepie that displays the content from a Facebook RSS feed showing stories with text and an accompanying image if available.

The URL of these images have an appended string before the actual image:

http://external.ak.fbcdn.net/safe_image.php?d=AQDZORAaPpbr5COr&w=154&h=154&url=http://example.com/image.jpg

Where "http://example.com/image.jpg" is the actual URL I want to show.

I would like to remove "&url=" and everything before it for any URL in the output HTML.

How can I do it? Thanks in advance.