Lately, I’ve been working on some WordPress projects for my clients and had this ‘Http Error’ when uploading images (only images) to the Media Library. What didn’t help?
– Switching to the browser uploader. (When I switched I had a Proxy Error and blank page instead.)
– Chmoding wp-content/uploads or the entire WordPress directory to either 755 and 777.
– Deactivating all plugins and switching to the default Twenty Fourteen theme.

You know why it didn’t work? Because these are not the proper step for fixing this specific issue. The problem is, WordPress 3.8 and 3.8.1 (maybe also some previous versions and future ones) uses ImageMagic instead of good old GD for image processing purposes (eg. making thumbnails of uploaded images, etc).

The trick is to either compile PHP with ImageMagic support (if you are on a shared hosting without command line access this doesn’t help because you can’t change your hosting provider’s PHP) or installing a great WordPress plugin Force Regenerate Thumbnails which forces your WordPress to use GD library for image processsing and also regenerates broken thumbnails that you previously couldn’t do because of the error aforementioned. There is one catch, however. You need to have that plugin activated all the time because of the overriding image processing method it does.

I’m also contacting my host to switch to PHP version 5.5 and I hope it will help, because I don’t want that plugin to be installed all the time.