When converting images for web use it is often not enough to simply resize the image. In some cases the canvas (background) needs to be resized too to cater for layout issues.
In a recent project using Actinic e-commerce, I needed to provide my client with a solution that allowed them to resize a folder full of images of differing sizes and shapes, for use on the e-commerce site.
To keep things in columns this meant that after each image was resized, resulting in images of all shapes and sizes, all needed to be placed on a 400 x 300 canvas.
I found the free Faststone viewer more than up to the task (see http://www.faststone.org/).
This fantastic application allowed very tailored batch processing of the image, not only for image size and canvas size, but a host of other options too.
To help those with the batch processing, as well as my client Hoppers Jewellers I have produced a step by step guide on how to batch convert images using Faststone. You can download/view this publication here:
Hope this helps