If you want to resize your JPG images for the best web performance or create thumbnails for an image gallery check out iResizer (http://www.iresizer.com/) for Mac OS X.
With it you can scale an image without changing visual content such as people, buildings, animals, and more. Just point to the source directory and choose whether you want to have the source images resized or have completely new images.
Normal resizing affects all pixels uniformly when you scale an image, iResizer resizing mostly affects pixels in areas that don’t have important visual content. The app lets you shrink or enlarge images to improve a composition, fit a layout, or change the orientation. It also can be used to remove a portion of an image in a consistent way. For example, you can turn a landscape picture into a square picture and close up the space between people in a image if they’re too far apart.
With iResizer- — which was recently revved to version 2.3 — you can mark important elements in an image using a green marker that can be used to, for instance, protect people in the image. A red marker lets you choose which features of the image should be discarded.
iResizer is easy to use. Load the image you want to resize. Make a rough selection around the area you don’t want to be affected when you resize the image. You can also, if you wish, make a selection around the content you want to discard (discard masks are ignored when enlarging an image). Press the Smart Resize button. iResizer users “intelligently” generated textures pulled from the surrounding image data to scale the image. You can then save the result.
iResizer isn’t for everyone. But if you have any of the image manipulation needs mentioned above, it’s an effective and reasonably priced tool at $19.99 for a personal license.