確保傳到後臺的是純base64字串而不是以data開頭的

   //base64圖片上傳
    public function uploadCompressImg(Request $request)
    {

        $base64 = preg_replace("/\s/",'+',$request->input('img'));
        $img = base64_decode($base64);
        $disk = \Storage::disk('qiniu'); //使用七牛雲上傳
        $img_name = date('Y/m/d-H:i:s-') . uniqid() . '.png';
        $filename = $disk->put($img_name,$img);//上傳
        if(!$filename) {
            return $this->apiResponse(500, '上傳失敗');
        }
        $img_url = $disk->getDriver()->downloadUrl($img_name); //獲取下載連結
        return $this->apiResponse(200, '上傳成功',$img_url);
    }