1. A skew detection apparatus, comprising: a data storage device to store a document; a hardware processor to: generate a first estimate of a skew angle based on an alignment of peripheral boundary points of the document or an alignment of peripheral boundary points of foreground content of the document; generate a second estimate of the skew angle based on an orientation of foreground or background content in an interior of the document; generate a combined estimate of the skew angle, based on at least one of the first and second estimates; and determine a confidence value of the combined estimate of the skew angle, wherein to determine the confidence value, the hardware processor is to: determine an angle of a line joining two pixels for each side of the image; calculate a side confidence value for each angle; combine the angles by clustering them into groups; calculate a group confidence value for each group based on a sum of the side confidence values of the angles in the group; select the group having a highest group confidence value; and estimate the confidence value based on a comparison between the highest group confidence value and a second highest group confidence value.