If you like to download images from time to time on the Internet you are probably using a tool for that as it makes the mass-downloading of images more comfortable.
While it is certainly possible to simply right-click on the images that you want to download and select the save option, or snag them out of your browser cache where they automatically land when you view them in the browser, it is usually way more comfortable to use a program that automates part of the downloading for you.
Imagine a page with 40 or so images displayed on it that you want to download all. Instead of having to right-click repeatedly, save the whole page, or extract the images from the browser cache, you could use an extension like Image Downloader for that to speed up the process significantly.
You simply click on the extension's icon in the browser's address bar when you want to download one or multiple images on that web page.
Image Downloader for Chrome
The extension displays a thumbnail view of each image that it has found on the page, with options to download all of them, or only select ones. It is easiest to use if you want to download all images as it requires only two clicks to do so. Click on the extension icon first, and then on the download button in the popup window that opens up.
You can filter images manually using checkboxes on the page, or use the url filter at the top to do so. This can be handy to download only specific images, e.g. only those hosted at a specific site or folder on that site. The filter supports regular expressions which you need to activate though before that options becomes available to you.
You may also specify minimum or maximum widths for the images that you want to download. This can be useful to prevent the downloading of image thumbnails for instance.
The settings of the extension, available after right-clicking the icon and selecting options from the context menu, allow you to modify how the images are displayed in the popup window. This includes modifying the window width, the minimum and maximum width of the images, and whether you'd like them sorted by url.
The extension works well on many different sites, from Imgur over Google Plus to Pinterest.
Update: The browser extension has not been updated since 2014 but it still works fine on many sites at the time of publishing this update.