Help How can reinstall my stock gallery app on my rooted device; it keeps on saying "App not installed" ?

[Android Question]

I uninstalled my stock gallery app, but thankfully I made a backup. Then I tried to reinstall it by placing it in the system/app folder and setting the permissions to read-write, read, read, but with no success. Here is a screenshot i have taken. Can someone here help to reinstall my stock gallery app ? I would really appreciate it.