Adjusting data for photographed images includes detecting a reference image in the data, where the reference image contains a detectable uniformity and adjusting the data according to the reference image. The reference image may be a uniform grid pattern of dots preprinted on paper. A paper type may be determined prior to adjusting the data according to the reference image. The paper type may be determined according to spacing and/or patterns of the dots, and/or layout of page areas covered with dots. Adjusting the data may include removing effects corresponding to a folded corner, a removed corner, an obstructed corner, lens flare spots, and/or a shadow. Positional coordinates of the data may be adjusted by normalizing the grid through a non-linear transformation that eliminates curvature of the grid and/or distortions based on perspective.