First option is to go on the image and by pressing on the image by left mouse button drag it into a new tab of your browser. In the new tab press the right mouse button and you will get the option save as.
But some of them cannot be downloaded by this method so here is the ultimate method
Go to the web address in your browser where the image is present and press print screen present in the key board and then go to paint and there paste it. You will have the image of whole of the page. Just crop the required image using a good photo editing software.