Making a circle from a square image

I've got a simple website for myself and i added square images. I used CSS to make these images a circle and make them rotate as soon as the mouse hovers over them. the problem is that the cirlces aren't completely round. At the top, bottom, left and right a little bit is cut off showing that it used to be a square. I also have bootstrap on so i can make tables. the 3 images are within those tables. The problem is that if i change anything about that it puts the third image under the rest of them. I have been trying alot of things but i just can't fix it. Hope someone here know's better than me. I have a picture but i can't upload it due to my lack of reputation.