Images uploaded to the image library are automatically cropped to smaller thumbnail, screen preview, low and medium resolution sizes. You therefore only need to upload the one high resolution image and Brand Toolbox creates the other versions.
These versions remain at the same aspect ratio as the original image. Note however that your particular instance may have other preset size versions.
For example, PowerPoint 4:3 (1024 x 768px) and PowerPoint 16:9 (1024 x 576px) versions of all images are also available for download. As the ratio of these sizes may differ from the original image, the images need to be re-cropped manually by the user after uploading.
To crop the image: