I'm looking for a way to only set the width of a thumbnail size and let the height set auto. So if I have two images. One is 600px/420px and one is 600px/600px. I want to set only the width of the thumbnail to 200px so wordpress crops the thumbnails of the above dimensions to 200px/140px and 200px/200px. Any ideas?
In your theme's functions.php file:
In a template or the like: