What is the difference between fit and fill?

The Fit setting will resize an image to fit within the bounds of its container with no cropping. 

The Fill setting will expand an image to fill the whole container, which may result in some cropping depending on the dimensions of your container and the image you send into it.

For the best results, try using Fit for logos, and Fill for photography.

Note: This option is not available for Static Image Objects (non API).