I continue to find the Preview application to be a handy little tool. Its not that Preview supports an enormous feature set for working with images, as much as each time over the last few months that Ive look to the Previewer to help me out, it did.
The first time this came about I simply needed to resize an image to post on this blog from the Tools menu, click Adjust Size and save the file, thats it, done (and of course it can preserve the aspect ratio). My most recent encounter was when I needed to convert a file type from JPG to GIF. Again, a few clicks and its done open an image, from the file menu choose the Save As option and from the dialog box select the image type. The figure below shows the supported file types; notice you can even save an image as a PDF.
By no means a full-fledged image editing program, and never intended to be, Previewer is still much more than its name suggests.