ZenFotomatic has three modes for setting the output photo size...
Set the width and the height for your output photo in pixels.
Set the width and the height for your output photo as a percentage of the original photo size.
Aspect Ratio Size
Set the aspect ratio of the output photo ie. 1:1, 4:3... In addition you can set the maximum width and height in pixels. If the original photo is smaller than the maximum size, the photo will not be upscaled.Fitting
Crop to Fit (Left)
The original photo will be cropped to fit your chosen photo size. This is the recommended setting for auto cropping.
Pad to Fit (Right)
Extra padding will be added to make the original photo fit your chosen photo size. The padding color is set to the backdrop colour.