When the profile pictures are not passed on from Moodle to Collaborate the problem is most likely that your site is preventing users from seeing the profile pictures without a login. (Collaborate does not have permission to access and show the profile images because they are not public)
You should check your site's security settings Site administration > Security > Site security settings and the following settings: Force users to log in forcelogin and Force users to log in to view user pictures forceloginforprofileimage Both of these should be disabled. (Please notice that disabling the forcelogin setting will slightly affect user's login process.)
If you use Collaborate plugin it would be also good to check the plugin configuration to confirm that your site is configured the use REST API instead of SOAP API as SOAP is deprecated and it might cause issues with the profile images. You can find the plugin configuration by navigating to Site administration > Plugins > Activity modules > Collaborate Ultra If the fields under REST API settings are empty you can create ticket in Behind the Blackboard and ask Blackboard Support to send you REST credentials.