RMS is used to store data that needs to be loaded again later, like e.g. variables that is input by the user, or highscores achieved in a game.
In my opinion it would only make sense to store images in RMS, if they have been edited by the user. But even then, I'd probably go with saving them on the file-system instead.
A MIDlet cannot come with data pre-defined in RMS. In order to put data into RMS, you need to get that data from somewhere first, e.g. inside the jar file resources folder, or downloaded from the web.