attachment_fields_to_edit is still there in 3.6. It is in /wp-admin/includes/media.php in a couple of places. Perhaps usage has changed, or something has changed that has broken your code but without that code it is impossible to tell.
Limit image upload
It’s actually a feature, not a bug! 🙂 WordPress will use (actually image_get_intermediate_size() function) a image already cropped if the width or the height matches the required dimension, and the required dimenssion for image editor is 900×450, EXACTLY your defined width. A workaround will be to adjust your custom image size to 205 x 499 … Read more
Custom media uploader not showing library
How can I upload to wp media library by foundation zurb ajax
Rename attachment filenames to attachment ID on upload
Edit User Profile From Front End
Take a look at Otto’s Dynamic Image Resizer plugin This plugin changes the way WordPress creates images to make it generate the images only when they are actually used somewhere, on the fly. Images created thusly will be saved in the normal upload directories, for later fast sending by the webserver. The result is that … Read more
wp_handle_upload: get custom checkbox value from media uploader
Attach media to post by media category