Permission on Media file

I want to modfiy the permission on the library MEDIA.
All can use all Media in their layout.
The owner and the group wil be inside can have all rights.
And this for all existing file in media and new file added
Can you help to implement that?

Assuming you’re using 1.8 CMS, you can set the default media and /or layouts permissions to group / group write in CMS settings.