I want to be able to upload a 1000 x 1000px image as a featured image on a post but then be able to crop it to the required featured image size. Any way to enable this?
This can be achieved by either creating an image size using
<?php add_image_size( 'my-image-size', 1000, 400, true ); ?> or you can implement the Aqua Resizer to your theme/plugin. Aqua Resizer works almost in the same fashion as the good old TimThumb, but instead saves the image as a correct image size in WordPress using WordPress' intermediate sizes methods.
This is called Post Thumbnails. It was set by your theme.
You can open file functions.php and search for
set_post_thumbnail_size. If found, change it :
If not found, just insert new line.