1. A computer-implemented method, comprising: using one or more computing devices, receiving an input image comprising a digital image photograph of a customizable product with markup; using the one or more computing devices, partitioning the input image 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 the markup 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.