Draw a square with the Frame or Graphic Frame Tool and place the image into.
if the image is not placed:
1. Draw out a graphic frame while holding the SHIFT key
2. Place the image in the frame.
3. Chose one of the fitting options to fit (or not to fit) the placed image to the frame.
If the image is already placed:
Select the container frame.
1. Set the reference point to your needs before. There are 9 options.
2. Unlock the lock for the height and width input fields if it is locked.
3. Type in the same values for width and height for the container frame.
4. Chose one of the fitting options to fit (or not to fit) the placed image to the frame.
There's also the Convert Shape feature in the Pathfinder panel–in case you are trying to convert an existing frame or fix a frame that is out-of-square