To copy an image from a webpage, drag it from one browser tab over to the Trello browser tab and drop it into a Trello list, and it will create a new card. You may also drop it into an existing card, and the image attachment will be added to that card. (*Note that some websites don't allow "hotlinking" to their images and this technique may not work with every website.)
You can also right-click an image on a page, select the Copy Image option, come back to Trello and select Ctrl+V (Windows) Cmd + V (Mac) and the item will appear on your Trello board.
To copy a website, highlight the address of the site, and click and drag it over to the Trello browser tab. Locate a list or card where you would like it to appear and “drop” the link there. Sometimes sites will import a thumbnail image along with the site link.