wx.saveImageToPhotosAlbum()能否保存项目中的图片？

wx.saveImageToPhotosAlbum({

    filePath: ‘/images/20170921.png’,

    success: function () {

        console.log(“保存成功”)

        wx.showToast({

            title: ‘保存成功’,

            icon: ‘success’

        })

    },

    fail: function (e) {

        console.log(“保存失败”)

        console.log(e)

    }

})

这样用会开发工具报错  saveImageToPhotosAlbum:fail file not found