This is the body of the selector that is specified in NSThread +detachNewThreadSelector:(SEL)aSelector toTarget:(id)aTarget withObject:(id)anArgument

    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    while (doIt)
    {
        if (doItForSure)
        {
            NSLog(@"checking");
            doItForSure = NO;

            (void)gettimeofday(&start, NULL);

            /* 
                do some stuff   */

            // the next line prints "_NSAutoreleaseNoPool():" message to the log
            CGImageRef screenImage = UIGetScreenImage();


            /*
                do some other stuff */

            (void)gettimeofday(&end, NULL);

            elapsed = ((double)(end.tv_sec) + (double)(end.tv_usec) / 1000000) - ((double)(start.tv_sec) + (double)(start.tv_usec) / 1000000);

            NSLog(@"Time elapsed: %e", elapsed);

            [pool drain];
        }
    }

    [pool release];

Even with the autorelease pool present, I get this printed to the log when I call UIGetScreenImage():

2010-05-03 11:39:04.588 ProjectName[763:5903] *** _NSAutoreleaseNoPool(): Object 0x15a2e0 of class NSCFNumber autoreleased with no pool in place - just leaking

Has anyone else seen this with UIGetScreenImage() on a separate thread?