add width and height to images in a string

I have a sting value that is HTML with images in it. I need to parse the images and add a height and wisth. How do I do this?
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<a rel="nofollow" target="_blank" href="http://s361.photobucket.com/albums/oo54/thebayarearocks/?action=view&amp;current=IMG_3111.jpg"><img src="http://i361.photobucket.com/albums/oo54/thebayarearocks/IMG_3111.jpg" border="0"></a>
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<a rel="nofollow" target="_blank" href="http://s361.photobucket.com/albums/oo54/thebayarearocks/?action=view&amp;current=IMG_3119.jpg"><img src="http://i361.photobucket.com/albums/oo54/thebayarearocks/IMG_3119.jpg" border="0"></a>
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Needs to be:
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