Yes, please see the newly released CB primer book. It explains how to use the "Maintain Aspect Ratio" parameter for image fields to have perfectly squared images on upload.
Also it would be great, that if a user uploads an avatar image, that he mandatory sees a cropping functionality, which forces him to crop a picture into a squared format with a min and max size (just like on Gmail for example). Is that possible?
This is not possible yet, but is planned for a later release.