1. A computer-implemented method, comprising: capturing a sequence of images using a camera of a computing device; generating first gradient histogram data for a first image included in the sequence of images; determining a first sigma value corresponding to the first image by analyzing the first gradient histogram data, the first sigma value representing a first variance of gradient values in the first gradient histogram data; generating second gradient histogram data for a second image included in the sequence of images; determining a second sigma value corresponding to the second image by analyzing the second gradient histogram data, the second sigma value representing a second variance of gradient values in the second gradient histogram data; stopping the capturing of the sequence of images when the first sigma value is greater than the second sigma value; and selecting the first image from the sequence of images when the first sigma value is greater than the second sigma value.