A system receives a page request for a requested document, where the requested document specifies a set of first images as being presentable within the requested document. In response to the received page request, the system modifies the requested document and generates a modified document. The modified document specifies a second image that is to be generated based on the set of first images. The system generates the second image, based on the set of first images, and provides the modified document and access to the second image. The second image is an aggregation of the first images, which are represented within the second image as sprites to be rendered with the modified document. The modified document may use these sprites by specifying regions within the second image as being presentable within the modified document, where these regions correspond to the first images.