framework/i18n/Formatter.php
public function asImage($value, $options = [])
    {
        if ($value === null) {
            return $this->nullDisplay;
        }

        return Html::img($value, $options);
    }
public function asImage($value, $options = [])
    {
        if ($value === null) {
            return $this->nullDisplay;
        }

        return Html::img($value, $options);
    }
Formats the value as an image tag.
@param mixed $value the value to be formatted.
@param array $options the tag options in terms of name-value pairs. See [[Html::img()]].
@return string the formatted result.