It encodes any type of image (probably even other types of files). The decoding, though, only works for a few types (works for PNG and JPEG, doesn't work for ICO and SVG). On a side note, although it has a nice visual interface, its usability for encoding is poor: it's necessary to download the image, open the extension, upload the image to it, then generate the code, while other add-ons allow a much simpler conversion by right-clicking (context menu) on a web image. The encoding could be done within the context menu, leaving the stand-alone interface just for decoding.