I've searched high and low for this but think the answer I seek is being buried by the more common questions.
I am developing a theme for a client that has two specific image sizes (100x127 for thumbnail, 300x380 for medium). I have the media settings cropping like this when an image is uploaded, but if the user goes in to edit a thumbnail it doesn't re-crop to the sizes specified in media settings.
What I am ideally looking for is either a plugin or something I can add to functions.php that will restrict the crop "draw" feature to the aspect ratio and then when the crop button is hit, will automatically resize the thumbnail to 100x127.
Does anything like this exist? I don't even want the end user to have the option of entering in custom pixel sizes or aspect ratios. I'd rather that menu went away entirely.