Devise\Media\MediaPaths::imageCaptionPath PHP Method

    public function imageCaptionPath($imagePath)
    {
        $imagePath = $this->makeRelativePath($imagePath);
        $parts = explode('.', $imagePath);
        array_pop($parts);
        // dropping extension
        $pathWithoutExtension = implode('.', $parts);
        return $this->basepath . $pathWithoutExtension . '.txt';
    }