I just figured out that - instead of using a UIImageView to show an image - I use an UIWebView, it uses much less memory. Does that make sense for anyone?
What I did was to get an ordinary .jpg file with about 280kb in size and show it on a simple app with just an UIImageView. Looking at Instrument's Object Allocations tool, the application's memory footprint was about 3MB.
Then I removed the UIImageView and added an UIWebView with the following code:
NSString *html = @"<html><body style='margin:0;'><img src='my_test_image.jpg'></body></html>";
[web loadHTMLString:html baseURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] bundlePath]]];
and then the memory usage dropped to around 700kb.
Any thoughts?