setAreaOfInterest method of the RTRTextCaptureService protocol
Sets the search area on the frame.
The size of the area of interest affects performance and the speed of convergence of the result. The best result is achieved when the area of interest does not touch the boundaries of the frame but has a margin of at least half the size of a typical printed character.
The rectangle specifying the area of interest. Pass CGRectZero as this parameter to select the default area of interest that covers the whole frame (not recommended).