Also available for Firefox: https://addons.mozilla.org/firefox/addon/double-click-image-download
Download images directly via various interactions, including double-click, a hovering button with drag&drop support, and a hotkey. Includes the ability to rename downloaded images with patterns.
Note: does not support resolving thumbnail links to full size images. Alt-click such links to use the browser's own link downloading ability.
Please check the linked homepage for more complete information. Issues can be filed on the linked support site.