Scroll down the species page until you see the full-sized or thumbnail version of the image that you want to compare.  Click on the image and it will appear full size in this window.  By opening two or more comparison windows simultaneously, you can compare images of features of several species at once.  If you want to see more detail, click on the full-sized image in this window and a new browser window will open with the high-resolution version of the image.  By zooming in on that image, you can observe the maximum level of detail available.