By default, bbpress shows the user’s Gravatar using his/her email ID. This can be changed by avatar-upload, a plugin for bbpress. This plugin for bbpress allows users to upload an avatar (gif, jpeg/jpg or png) image to bbPress, and provides template functions to display the uploaded image. Other features :

• Admins can configure maximum allowed file size (bytes) and dimensions (pixels) of images from within the admin page (credit: Sam Bauers).
  • Images that exceed maximum dimensions are automatically resized (and sharpened if truecolor images).
• Anybody with the ‘moderate’ capability can upload another user’s avatar

User uploaded images can be used to show the user’s avatar in bbpress forums.

Download from : http://bbpress.org/plugins/topic/avatar-upload/