iPhone and OpenCV
OpenCV does indeed work on the iphone. Use the configure script here to compile the library: cross compiling for iphone
You just have to cross-compile just as you do your apps.
OpenCV now (since 2012) has an official port for the iPhone (iOS).
You can find all of OpenCV's releases here.
And find install instructions here:
The latest build script from Computer Vision Talks works great for Xcode 4 and iOS 4.3 . I have tried the script myself and it is just awesome!