An "ImageFit" slide is where the image that is being uploaded is actually altered in either the X or Y dimensions to fit the panel. For clarity:
If the destination panel is 640x600
If the image is 640 x 200 then the image will be stretched in the Y axis to become full panel - in other words, the 200 will be stretched to 600.
See the images below, original is first image.
If the image that you are loading is 800 x 600 - then the image will be squashed in the X axis to 640 wide - in other words, the Y dimension will remain the same but the 800 will be reduced to 640 pixels
If the image you are loading is 600 x 400 - then the image will be stretched in BOTH directions - from a width of 600 to a width of 640 and from a height of 400 to a height of 600 - as in the example images below
This image widget is particularly useful if you have images that are not precisely the same as the panel size but you want them adjusted to fill the whole panel.
Use the browse button to locate the image that you want to upload. It will be added the content library for use later on in other slides. You can add duration, schedule and background color to this slide type as well.