Make thumbnails square

I'd like to have my thumbnails square, like I upload them.

This is the code:

@media only screen and (min-width: 801px) {
	.featured-posts article .entry-image,
	.category-posts article .entry-image,
	.format-posts article .entry-image,
	.latest-reviews article .entry-image {
		height:220px;
		overflow:hidden;
	}

Even if I set height to auto it doesn't work.

What to do?