If you are using the Admin portal for Learn, you may want to add image avatars for your courses and user accounts.
The pictures will crop or load better depending upon their dimensions.
For a picture you want to upload, you can find its dimensions.
Here is a helpful article on that:
You can scroll down to the Saved File section.
Here are the values for the classroom and account avatars respectively:
256px x 144px
149px x 149px
However, you may try other values that might stretch or constrain the picture.