ImageDownloader is an open-source portable tool which enables batch downloading images from Reddit and Imgur.
A simple tabbed interface allows choosing your source subreddit or Imgur album.
The Reddit tab has more options. You can choose to main page, Top, New, Rising or Controversial. A time filter enables grabbing posts from the last hour, day, week, month, year or all time. You can optionally skip albums, NSFW posts and more, and specify the number of posts to get.
Both the Reddit and Imgur tabs allow filtering by maximum and minimum height and width, or by aspect ratio.
This is simpler than it sounds. Here's how quickly you can get started.
1. Click the Reddit tab.
2. Type wallpapers in the Subreddit box.
3. Click "Select" and specify an empty folder somewhere.
4. Leave all the other settings at their default.
5. Click Download and watch as the status panel displays what's happening.
A bonus "Local" tab enables copying files from one local folder to another, again filtering by file size or aspect ratio.
ImageDownloader worked as advertised for us, but beware: the Imgur downloader uses Imgur's API and has IP and client limits on the number of requests you can make. These don't seem too restrictive - when we checked we had a personal limit of 500 API requests which seemed to be reset multiple times a day - but if you want to batch-download the entire site, or others are making heavy use of the client, it might stop working for a while. You can use a custom Imgur ID of your own if you run into trouble.