1. A computer-implemented method for creating a mosaic based on a reference image, comprising: providing a first interface on a content sharing website that allows users to interactively create mosaic tiles for insertion into respective portions of a mosaic based on a thematic reference image; managing the interactive creation of a plurality of user-created tiles on the first interface, comprising, for each of the plurality of user-tiles: painting at least a portion of a respective initial canvas in a second interface using a respective background color prior to the respective user-created tile being interactively created to increase a likelihood that the respective user-created tile will be inserted into the mosaic, based on one or more available portions within the mosaic and a corresponding one or more portions of the thematic reference image; and generating the respective user-created tile by creating a customized image based on a plurality of user selections on the respective painted initial canvas in the second interface; populating at least a portion of the mosaic with the plurality of user-created tiles created using the second interface, by operation of one or more computer processors, comprising: determining a suitability value between each of the user-created tile in the plurality of user-created tiles and a corresponding portion of the thematic reference image; and inserting a particular user-created image into the portion of the mosaic based on the determined suitability value, based on at least one of (i) a first proximity in the mosaic to a first user-created image by a same author, (ii) a second proximity in the mosaic to a second user-created image with a same title, and (iii) an effort value calculated for the particular user-created content.