[TYPO3-english] Resizing images from an extension

[Martin Bernt Rud]

Hi list,

I have made some kind of wall extension where users can post a message and
attach an image file. I now want the extension to resize the image placed in
the uploads/tx_myext-folder to maximum 400 px width. In other words I
_don´t_ want TYPO# to create a thumbnail in the typo3temp-folder and keep
the original file in the  uploads/tx_myext-folder. _Instead_ I want the
extension to resize and overwrite the original file (to save space on the
webhotel).

How do I do that?

Regards,
Martin