Image resources for iOS
Have you tried to simply load the image using:
UIImage * someImage = [UIImage imageNamed: @"someimage"];
(assuming your have an image named 'someimage' in you project, for example someimage.png)
The code will automatically pick retina/non-retina versions depending on the platform.
If the problem is that the TIFF are created, check:
In latest version of XCode, go to the Editor menu, then select "validate settings", which should remove that artwork combination.
Multipage TIFFs are only for OSX; they don't work on iOS.
So you need to stop trying to access resources that are, by their very nature, inaccessible, and do things the right way!
You need to open the project that generates the external resources bundle, select the target, go to Build Settings and then the Deployment sub-heading, and set "Combine High Resolution Artwork" to No. Then recompile the external resources bundle.
In your main project you should now be able to read in the PNGs in the normal manner.