When claiming your profile, or creating a partner profile you can add a photo of yourself or a logo of your business or organization. When creating challenges you can also add a banner image to that as well.
Here are the photo dimensions that work best:
Profile image
The ideal ratio is 1:1 (square images) and the dimensions are as follows:
Profile Image:
Minimum: 120 x 120 px
Maximum: 360 x 360 px (Recommended)
Featured Challenge Banner Image
The ideal ratio is 16:9 (rectangle) and the dimensions are as follows:
Challenge Banner:
Minimum: 414 x 240 px
Maximum: 1242 x 720 px (Recommended)