1. A method for defect detection, comprising: generating a first image of a first area of an wafer; registering the first image with respect to a computer aided design (CAD) data to provide a first registered image; generating a second image of a second area of an wafer; registering the second image with respect to the CAD data to provide a second registered image; detecting defects in response to a comparison between the first registered image and the second registered image; and generating defect location information in CAD coordinates wherein registering the first image comprises: dividing the first image into multiple first image blocks; locating within each of the first image blocks at least one registration target; determining a first block offset between each of the first blocks and between a corresponding block represented by CAD data; and determining an offset estimate for the first image in response to multiple first block offsets; wherein locating comprises: evaluating a quality of registration achieved by utilizing a certain first image block and selectively providing a first image block offset estimate in response to the evaluated quality of registration.