1. A computer-implemented method, comprising: using the one or more computing devices, partitioning an input image of a customizable product into a plurality of image regions based on color and color differences of pixels of the input image and generating region information that specifies how the input image is partitioned into the plurality of image regions; based at least in part on the region information that specifies how the input image is partitioned into the plurality of image regions, determining data that represents at least a particular portion of a markup in the input image; wherein the data that represents at least the particular portion of the markup in the input image comprises information about a set of image locations that are within the particular portion of the markup, and indicates a color of the particular portion of the markup embellished in the input image; based at least in part on the data, determining rendering instructions for rendering a computer-generated visualization of the customizable product; and sending the rendering instructions for rendering the computer-generated visualization of a customizable product to a web server; storing, in data structures in computer memory, information describing the plurality of image regions, the data structures including a first data structure which identifies, for each image region of the plurality of image regions: a representative color value identifying a color that represents the image region; a size of the image region; or a single location assigned to the image region.