A media analysis tool is provided for defining dynamic regions of a digital media segment. The dynamic regions may contain at least part of a visible feature of the segment. Correlation of the defined regions with external data quantifying attention of a subject viewing the segment to locations on the screen provides measures of interest level and attention to visible features in the segment. The dynamic regions may be defined in only some of the frames of a segment. The dynamic region may be interpolated or extrapolated for frames in which it is not explicitly defined.