Lots of ways, what you said is a good one. Select a graphic (as GM) and press Shift-Z, this shows a full size pop-up with dark background called a lightbox. Add the image to a Handout, and press "Show To Players". Here in this method the players can go back and re-open it when they want to look again later. Make the image a PAGE of it's own, drag-and-drop the Players ribbon to the page. Pro Users with API access install the "Color Emote" API from the One-Click and make a simple macro, good way to put any on-map picture into the Chat log. Really fantastic for games that look at the roll20 chat a lot. I use all of the above. In different circumstances.
