Case sensitive file names (not in the simulator)

This is something I just ran into dealing with images on buttons.
The image on the file system is "stepdone.jpg"

In the simulator the code that worked to load the images is;

[thisUIButton setImage:[UIImage imageNamed:@"stepDone.png"] forState:UIControlStateNormal];

This did not work in on a provisioned device. As you know file names are case sensitive. But it appears that the Simulator was not picky

Actual required code:

[thisUIButton setImage:[UIImage imageNamed:@"stepdone.png"] forState:UIControlStateNormal];