1. A non-transitory computer-readable medium containing instructions which, when executed by a computer, perform a process comprising: receiving an image of a document captured by a mobile device; processing the image to determine a set of image quality assurance (IQA) scores; performing a computation relating to the set of IQA scores to obtain at least one compound IQA score, wherein the computation includes combining a subset of strongly correlated IQA scores in the set of IQA scores into a compound IQA score, and wherein the subset of strongly correlated IQA scores is associated with a common image defect; determining if the image meets a predetermined standard of image quality based on the at least one compound IQA score; and if the image meets the predetermined standard of image quality: assessing a usability score of the document in the image to ensure that the document belongs to one of a set of supported categories of documents; and outputting the at least one compound IQA score and the usability score; otherwise, characterizing the image as unusable.