You may want to take a look at irfanview which is got quite powerful command-line support for manipulating images. It can be run in silent mode, from perl, and it all works quite well.

To resize image, use the resize-switch:
(From the help docs)
/resize=(w,h) - resize input image to w (width) and h (height)

In reply to Re: Resizing Jpegs in TK by ldln
in thread Resizing Jpegs in TK by K_M_McMahon

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