Turns out you have to use UIGraphicsBeginImageContextWithOptions…

This doesn’t work on the retina display:
(void)captureThumbnail:(id)theViewToCapture
{
UIGraphicsBeginImageContext(((UIView*)theViewToCapture).frame.size);
[((UIView*)theViewToCapture).layer renderInContext:UIGraphicsGetCurrentContext()];
theImage.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}

This does work on the retina display:
(void)captureThumbnail:(id)theViewToCapture
{
UIGraphicsBeginImageContextWithOptions(((UIView*)theViewToCapture).frame.size, NO, 0.0);
[((UIView*)theViewToCapture).layer renderInContext:UIGraphicsGetCurrentContext()];
theImage.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}