See http://blogs.msdn.com/calvin_hsia/archive/2005/08/11/450587.aspx

>Hi all
>
>Does anyone knows the algorithm that lets me resize an image with a width/height limit?
>
>What I want is to create thumbnails that fits in a 109x109 pixels image control. What I already know is that if the picture width and height is not > 109 then the image is not resized cause it fits ok.
>
>But when is not the case then some constant must be applied to widht and height to fit the image without loosing proportions.
>
>Any idea?
>
>Thanks in advance
>Héctor L.