Above the brightness controls is an “open in new browser window” button, and from there you can click the image to zoom in further. You also can use the browser zoom (ctrl + or ctrl -) to step zoom more finely.
Based on some advice from this forum, I installed this Image Viewer add-on for Chrome: https://chrome.google.com/webstore/detail/image-viewer/kcljlcpbfbkapegpifkodjdmdllgdlmk
I can then open an image in a new window, like @kiwifergus advises, and zoom or rotate it as needed to see as much detail as the image contains.