If you do not want your Clock skin image files to show up in Gallery, you can place a .nomedia file in the Clock skin folder.
To create a .nomedia file in the Clock skin folder, follow these steps:
1.Download ES File Explorer from the Google Play Store.
2.Use ES File Explorer to open the Clock skin folder.
3.Tap the Menu button menu button grey in the upper-right corner, and then select New.
4.Select File.
5.Enter the filename “.nomedia”, and then tap OK.