Replace default member avatar

function myavatar_add_default_avatar( $url )
{
  return get_stylesheet_directory_uri() . '/images/my_image.png';
}
add_filter( 'bp_core_mysteryman_src', 'myavatar_add_default_avatar' );

Replace buddyypress / wordpress avatar

//****************************************************
//****************************************************
//********** REPLACE DEFAULT WP USER AVATAR **********
//****************************************************
//****************************************************
add_filter( 'bp_core_fetch_avatar', 'my_bp_core_fetch_avatar', 10, 2 );
function my_bp_core_fetch_avatar ($avatar_img_tag, $params)
{

  if (
    (!empty($params)) &&
    ( ($params['object'] == 'user') || $params['object'] == '') )
  {
    //----- CALL IS FOR A USERS AVATAR -----
    $ImgWidth = intval($params['width']);
    $ImgHeight = intval($params['height']);
   
        
    $user_id = $params['item_id'];
    if (is_int($user_id))   //Ensure user ID is set
    {
   
      $ImageUrl = "ADD IMAGE URL HERE";

      
      if (strlen($ImageUrl ) > 0)
      {
          //WE HAVE AN IMAGE FOR THIS USER TO OVERRIDE THE DEFAULT IMAGE WITH
          
          //If there is a width and height specified then override styling to use object-fit: cover (fill area and crop image if needed)
          if ( ($ImgWidth > 0) && ($ImgHeight > 0) )
          {
            //Override the string with our styled img tag so image stays in correct proportion
            $ImgStyle = 'style="';
            $ImgStyle .= 'object-fit: cover;';
            $ImgStyle .= 'width: ' . $ImgWidth . 'px;';
            $ImgStyle .= 'height: ' . $ImgHeight . 'px;';
            $ImgStyle .= '" ';

            $avatar_img_tag = preg_replace( '/(<img src=")(.+)(" class.+)/', "$1$ImageUrl$3", $avatar_img_tag );      //Replace the url
            $avatar_img_tag = str_replace("/>", ">", $avatar_img_tag);                //Ensure it doesn't end with />
            $avatar_img_tag = str_replace(">", " $ImgStyle >", $avatar_img_tag);      //Add our special style to the end
          }
          else
          {
            //Use the original string and just replace the url
            $avatar_img_tag = preg_replace( '/(<img src=")(.+)(" class.+)/', "$1$ImageUrl$3", $avatar_img_tag );      //Replace the url
          }
         
      }
    }

  }

  return $avatar_img_tag;
}

/* THERE IS ALSO THIS FUNCTION IN CASE EVER NEEDED:
add_filter( 'bp_core_fetch_avatar_url', 'my_bp_core_fetch_avatar_url', 10, 2 );
function my_bp_core_fetch_avatar_url ( $avatar_url, $params )
{

	return $avatar_url;
}
*/