Currently, you can auto-resize a cell when you place an image in that cell. However, if the image is smaller than the cell dimensions, the cell does not automatically shrink to fit the image dimensions. You have to manually move the cell boundaries to fit an image. This would be a nice feature to add. 

Please see the screenshot below. In this example, I added an image which is smaller than the cell. In order to adjust the cell to auto-fit/shrink to the image then I have to move the cell boundaries manually. The arrows show how I have to move the boundaries to fit the image.