Here is tweak in windows 7 that will deny the write access to any removable media,
1. Press Windows logo button + R
2. Type "gpedit.msc" and press enter
3. Navigate to User Configuration > Administrative Templates > System > Removable storage access and on the right go for "Removable Disks: Deny Write Access" and double click on it and click on enable and click OK.
4. That's All. Restart your Computer to take effect.