There are multiple versions of this command. I'm leaning towards the graphicx version because it requires nesting within \rotatebox and \scalebox for rotation and scaling operations. It seems likes this would avoid duplicate code b/c we want those commands as well (#681).

There's a number of different options that \includegraphics can take. I think to start with support width and height are probably the easiest. The options are provided as a key-value list, e.g.

\includegraphics[width=320,height=240]{my-awesome-image}

While the file extension can be included, https://www.sharelatex.com/learn/Inserting_Images advises not to as LaTeX will look for all sorts of different image types with the same name. We probably want to avoid this behavior as it will be hard to implement in a performant way on the web.

A related command, \graphicspath provides a way to specify where to look for the images, e.g.

\graphicspath{ {images/} }

After skimming through the graphicx docs it's unclear to me whether the filename used in \includegraphics can include a full and/or relative path.