Image Smith is a batch image processing tool for Mac. It can be used to process multiple images at once. There are multiple actions that can be applied to an image and they are divided into categories. You can find them at the bottom of the application's window. These are Scaling, Format, Orientation, Crop, Color and Background. Each category contains different settings that you can modify. For example, under "Scaling", you will be able to modify the images' width and height, either by pixel number or percentage. Under "Format", you will be able to convert the images to other formats, including GIF, JPEG, TIFF and PNG, and set the JPEG quality. If you are converting GIF images, you can also choose to preserve the animation and transparency.
As I said above, you can add one or many images to the application by dragging and dropping them. All the settings that you choose will be applied to all of the images. You can see a list of the files added and even preview the settings before you process the images.
In short, this is a very handy application when you have to process multiple images at once. I found it is very easy to use and it worked well.
There is a 15-day trial available that should let you test the application fully before you have to purchase.