How do I take Transform lines off a collage

I am making a sports collage on cs6.

I select the image and bring it onto the background layer with the other images that make up the collage.

I press Cmd+T and size the image onto the collage. I then press Enter

There are rectangle lines around every single image I bring onto the Background layer.

How do I get these off my final image before printing?

Any help much appreciated.

Thanks, Denis