I think you're looking for the development tools in Safari, correct? If so, verify they're enabled by going to Safari » Preferences » Advanced and verify "Show Develop in menu bar" is checked. Then, in the webpage you want to view the images for, click Develop » Show Web Inspector in the menu bar and a new panel should appear on the lower half of your Safari window. In this pane, choose the resources tab and use the folders on the left to find the content you are looking for. You can control/right-click the filename to save them to your computer.
If there's just a specific image you wish to save on a webpage, in most cases you can also just control/right-click it on the page and choose to save it from the shortcut menu there without using the develop menus. This only works on certain images, though. Things in the background cannot be saved this way, and often webpages will be made to prevent this, and you'll need to use the develop menu to locate the images.