In auto-detection, auto-marking, and later on in motion tracking, the concept of "mask" is important. A mask is a small portion of an image that Photo4D uses as a guide to find similar portions elsewhere in an image. A mask has a square shape.
The size of a mask is determined by the size (in pixels) of feature points appearing in an image. The mask should include the portion of image that characterizes the feature point. For example, if the feature point is a dot of 7x7 pixels, the marks should be larger, e.g., 11x11, in order to include some background information.
To find out the size of a feature point, users may put the cursor at one end of a feature point and notice the cursor location at the upper-left corner of the Image window. Next, move the cursor to the other end of the point. The distance between these two cursor locations is usually a reasonable value for the mask size.