Resize Master is a simple Mac program that enables you to change the resolution of your favorite pictures. This utility is very simple to handle, supports batch processing and drag-and-drop action, works with various image formats, and immediately offers you the quality results you need.
The first thing you need to do before importing any images is to configure the output settings according to your needs. The application lets you choose from multiple image resizing techniques (to fit rectangle, scale by percent, etc.), watermark the resized pictures with text or images from your local directories, and edit meta information if necessary.
The most important advantage is the fact that the utility preserves the quality of the input photos and takes only a few moments to generate the resized pictures.
My only issue with this application is the fact that it supports a limited amount of output formats (JPEG, TIFF, and PNG). So, even though you can import PSD or BMP files, the app doesn't let you export the altered images with their original extension.
Cutting a long story short, it's worth installing this free program on your Mac only if the aforementioned disadvantage doesn't mean much to you. Otherwise, I'd suggest you to try other image resizing utilities on your Mac.