CCNA, CCNP, MCSA, CCNA Final Exam, All Answer Test Module With 100/100

I've customized my UISlider but my thumb image looks strange, I mean it's position not aligned by center: But should be like this: And here is code: UIImage *leftTrack = [[UIImage imageNamed:@"blueTrack.png"] stretchableImageWithLeftCapWidth:3 topCapHeight:0]; UIImage *rightTrack = [[UIImage imageNamed:@"whiteTrack.png"] stretchableImageWithLeftCapWidth:3 topCapHeight:0]; [slider setThumbImage:[UIImage imageNamed:@"thumbButton.png"] forState:UIControlStateNormal]; [slider setMinimumTrackImage:leftTrack forState:UIControlStateNormal]; [slider setMaximumTrackImage:rightTrack forState:UIControlStateNormal]; Where could be the problem? EDIT: I found solution of this problem. Thumb image background was transparent, and I've not seen that thumb image was not aligned by center: