The 'appearance' tab provides some image formatting options. You can set the alignment, resize your image and add a border.
Although you can resize your image by adjusting the dimensions it is best practice to optimise your image beforehand using an image editor such as Photoshop in order to maintain the best quality.
If you wish to add a border around your image you can do this by adding a '1' to the border field.
Once you have finished, click the 'insert' button.