I know that OpenCV was ported to Mac OS X, however I did not find any info about a port to the iPhone.
I am not a Mac developer, so that I do not know whether a Mac OS X port is enough for the iPhone.
Does anyone know better than me?
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.