iOS UIbutton weird bottom edge

Question

I'm just encountering a weird border for the UIbutton. I've added a button in the xib file and I've set for it an image but after running the project on the simulator it looked like this:

I haven't changed any property of that button and I haven't touched it in the code. Does anyone know why it is looking like this? and how can I solve it? Any help would be appreciated.

Thanks.

EDITED:

This is the image used for that button:

Answer 1

The image has a gray line on the bottom of it. Here it is blown up in Photoshop, with a red background added.

Answer 2

OK, try this image. I've removed the thin gray line from the bottom. It should fix your gray line :-)