BuddyPress Activity Plus is a popular BuddyPress plugin that allows members to share videos, phones and links on their activity stream. The plugin works good but earlier there were problems regarding its small photo embed size on activity stream.
But now no worries, the latest version of this plugin allows you to set a custom thumbnail image size which is shown when a user posts any photo or video file on BuddyPress activity stream.
Start by installing ‘BuddyPress Activity Plus’ plugin in BuddyPress
Once the plugin is activated, visit your admin area dashboard Settings -> Activity Plus page and scroll a little bit down.
You will be noticing, the plugin options for setting up custom oEmbed and image thumbnails size.