If the ImageDashboardItem's dimensions exceed that of the image it contains, the image is centered and shown full-size. Otherwise, the image is resized to fit into the ImageDashboardItem's dimensions.
The image is sized proportionally (without clipping), so that it best fits the ImageDashboardItem. If the ratio of height to width of the ImageDashboardItem is the same as the image's ratio, it will be resized to exactly fit into the ImageDashboardItem. Otherwise, the closest fitting side (height or width) of the image will be sized to the dashboard item and the other side (height or width) of the image is sized proportionally (leaving empty space).
Values listed by this enumeration are used to set the ImageDashboardItem.SizeMode property.