In Cocoa NSImage has a lockFocus method, that allows to draw images offscreen and combine them into one.
[img lockFocus]; //... [img unlockFocus];
On the iPhone, UIImage lacks the lockFocus methods, instead the following:
// Create new offscreen context with desired size UIGraphicsBeginImageContext(CGSizeMake(64.0f, 64.0f)); // draw img at 0,0 in the context [img drawAtPoint:CGPointZero]; // draw another at 0,0 in the context, maybe with an alpha value [another drawAtPoint:CGPointZero]; // ... and other operations // assign context to UIImage UIImage *outputImg = UIGraphicsGetImageFromCurrentImageContext(); // end context UIGraphicsEndImageContext();