Auto-Resize Free Photos to Max Size

When a person who is using a free account posts, they have a limitation of 1500 x 1500 as the dimensions for their photo. Typically they're posting across multiple platforms and are usually posting larger than that.

Would there be a way for when a free account is posted here, that it scales down the photo to 1500 x 1500 (or a properly ratioed version) so they don't have to resize it?