Adding more than two images to the project increases project accuracy through the benefit of least squares estimation. Each time the user adds a new image, they need to mark four or more reference points shared between the various images. iWitness has a built-in feature to help with this marking and referencing process. The rest of your previously marked feature points from image 1 and image 2 will appear automatically in blue on the newly added image. Viewing the previously marked feature points enables the user to quickly confirm and mark exact point locations.