Uses Imagemagick to resize images automatically.
Legend: 
Download

Report
I changed the contrib to show png-images with alpha-transparency in IE, thumbnails are only produced if the original file is newer than the thumbnail or if the thumb don't exist and if the either the width or the height of the original image are bigger than allowed. Additionally existing profiles (i.e. cameraprofiles) are removed from the thumb resulting in a smaller filesize.
The browser always gets the correct image-size (even if you wants to let imagemagick add a border to the thumb).
You can see this at a life-store: https://shop.entheogene.de/
(hint: take a look at it with M$-IE - some of the pictures/thumbnails are png with transparency).
Galen: Heh! I fixed the typo :-)
Realized that when you previewd the image after adding it didn't resize.
This is updated so it does :)
Galen
This contrib now has support for the admin section.
Please see thumbnails.admin.txt
Get catalog working before modding the admin section.
Support thread
http://forums.oscommerce.com/index.php?showtopic=94640
This an update to the information required to get this contrib working.
For extra support please visit the forums.
http://forums.oscommerce.com/index.php?showtopic=94640
What this does:
Uses Imageimagick to automatically resize images on the fly, the code is easy to implement but getting ImageMagick can cause some problems.
How it works:
When a customer view a product on your webpage it checks to see if it has been resized, if not it copies the image to a new directory(which you define) and then runs mogrify(part of ImageMagick) to resize the image. The customer then sees the re-sized image until they click on enlarge which then they view the original.
You can also use this package to do many many other things to your images(watermarks, text, adding images) rezise is just a small part of it
refer to the ImagicMagick wepage for more information.
Test ImageMagick seperately, refer to forum post above for more details, and please read everything :)
This only works for the catalog section, there are some notes of mine in the thumbnails.txt about implemtation into admin.
Galen
Hi All,
Please find enclosed for download a new file called thumbnails.txt .. the file has not association with what it does.. its just what I called it :)
I didn't write this but I will endeouvor to help you all out with this module.
The thumbnails.txt has step by step instructions to help you understand what the author of this contrib originally indended for you to do.
Galen
For continued support and questions I will try to answer them in the support forums below
http://forums.oscommerce.com/index.php?showtopic=94640
Uses Imagemagick to resize images automatically.