There are additional options available to you under the 'Appearance' and 'Advanced' Tabs in the 'Insert/edit image popup'. Some of these are explored below.
The option you select from this dropdown will dictate how this image will be 'aligned'.
Selecting the left alignment means that the image will display on the left hand side of the page, and any text that you add into the Text editor field will 'wrap' around the image on the right hand side, as with the image here.
You can enter whole numbers (in pixels) into the 'Dimensions' field to change the size at which the image displays. Click the checkbox for 'Constrain proportions' if you don't want the image to become distorted.
Enter a whole number in this field to dictate the amount of white space (in pixels) that will be left at the top of your image.
Enter a whole number in this field to dictate the amount of white space (in pixels) that will be left at the sides of your image.
Enter a whole number in this field to dictate the width of the border (in pixels) that your image will have.
If you select the 'Alternative image' textbox, you are able to replace the image with an alternative image when people 'mouse over' (hover over the image with a cursor) or 'mouse out' (remove the cursor from the image). To select a new image, click on the 'Browse' icon to the right of the 'for mouse over' or 'for mouse out' text field.