// URL des Bildes
id path = @"http://www.mobile-dev.de/images/stories/iPad_Simulator.png";
NSURL *url = [NSURL URLWithString:path];

// Bild laden
NSData *data = [NSData dataWithContentsOfURL:url];

// Bild im Dokumente-Ordner der App speichern   
NSString* savePath = [[NSString alloc] initWithFormat:@"%@/Documents/image.jpg",NSHomeDirectory()];
if ([data writeToFile:savePath atomically:YES])
{
     NSLog(@"Saved");
}
else
{
     NSLog(@"not saved");
}
[savePath release];

// Bild in eigener App anzeigen
UIImage *img = [UIImage imageNamed:@"image.png"];
UIImageView* imgView = [[UIImageView alloc] initWithImage:img];
imgView.frame = CGRectMake(10,10,img.size.width,img.size.height); // x=10 y=10 in original Bildgröße

[window addSubview:imgView];