1. A method, comprising: identifying a boundary for a feature of an image, the feature corresponding to at least one tile of a tiling scheme for the image; storing the feature in a cache when the feature is not already stored in the cache; tiling the image according to the tiling scheme to produce at least one tile; for each tile corresponding to the feature, replacing a portion of the tile occupied by the feature with a replacement image for the tile; and storing each tile in the cache that is not already stored in the cache.