PHP: fopen error handling

You should first test the existence of a file by file_exists().

try
{
  $fileName = 'uploads/Team/img/'.$team_id.'.png';

  if ( !file_exists($fileName) ) {
 throw new Exception('File not found.');
  }

  $fp = fopen($fileName, "rb");
  if ( !$fp ) {
 throw new Exception('File open failed.');
  }  
  $str = stream_get_contents($fp);
  fclose($fp);

  // send success JSON

} catch ( Exception $e ) {
  // send error message if you can
}

or simple solution without exceptions:

$fileName = 'uploads/Team/img/'.$team_id.'.png';
if ( file_exists($fileName) && ($fp = fopen($fileName, "rb"))!==false ) {

  $str = stream_get_contents($fp);
  fclose($fp);

  // send success JSON    
}
else
{
  // send error message if you can  
}