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I'm really sorry for the confusion. The image management page has changed a little bit. The changes include many new features, but some stuff has also been moved.

Please visit this page to find out how to delete your images, and to see the rest of the changes/features:
Well as the site grows, the needs of users grow too :( For what it's worth, the flash version has been the default for over a year.
I worked hard on making them look exactly the same, but the way the upload and process the image is entirely different.

The flash version works exactly the same across all platforms and browsers -- it even works in IE6. The HTML version will look the same as the Flash one on a modern browser, but you'll see the difference if you visit it in IE7-8.

The Flash version also processes the image before it's uploaded, so that it actually ends up uploading about half the data (for larger images), thus making them upload a lot faster. For the HTML version, it needs to upload the entire thing first, and then process it on the server side.

Overall, the Flash version provides a more standard way of uploading that works for everything. It's also way faster for larger images.

In time, the HTML version will be the default, and the Flash will be the backup (once I figure out how to do the client side processing in canvases and JS). However, right now, browser support for new HTML5 features just isn't there yet. Way too many people visit the site on outdated browsers, and I think it's important to provide the same experience across all browsers, no matter the version.
After some research and probing, it appears that the problem was isolated to one of Voxel's DNS recursors. This issue has been solved and all links should be working again.
The new version does indeed allow you to do this. In fact, you can choose files from your computer, then add URLs of images, and then drag and drop files and upload them all at the same time. Are you clicking "Done" after entering your URLs?
Determined that this is an issue with Plurk, and not Imgur.
Ok, well that settles it. If they display fine on other sites, then it has to be an issue/feature within Plurk. Have you tried talking with them about it?
Have you tried using the same links in another forum or something outside of Plurk?
It sounds like it could either be a problem with Plurk, or Imgur-specific code within Plurk that's displaying the thumbnail rather than the image. Unless you can link me to an image that's displaying the thumbnail no matter what you tell it...