Browser application programs may be prevented from performing cross-domain retrieval of anything other than image files. To enable browsers to pre-fetch resources utilizable by code executing in a browser-based programmatic environment, without having to wait for the environment, and the code, to be instantiated and make the cross-domain request themselves, the cross-domain resources can be transcoded into image files. Once retrieved, these “image” files can be retained locally in a browser cache and provided to the code executing in the browser-based programmatic environment from there much more quickly. Then the code can decode the “image” and extract the original resource file, which the code can then utilize. The transcoding of resources into image files can be performed by first determining the height and width of an image file that will result in the least amount of wasted space when the resource is transcoded into it.