Participants (or their parents) can upload an image to replace their icons. 

Here's what it looks like on the participant pledge page:
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Here’s what it looks like on the bottom of the main campaign page (if the participant list is not hidden):

Admins can change any participant image by going to the Groups & Participants tab and clicking on "Manage Participant". 

Here's how:

How it works for a participant to change their own image:
When participants receive their invitation email, there will be a special link for them to upload an image. No account creation or passwords are necessary.

Here's what it looks like. Instead of {{manage_participant_url}}, their link will appear there:

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Here’s your private profile management page (Do NOT share this with anyone!):

{{manage_participant_url}}

* Upload a profile picture

* Share by email and text message

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Once they click on that special link, it will open their Manage Participant page where they can add a photo: