Catching Elephant is a theme for Tumblr.
Please look through all the answers here before asking a question. The same questions keep coming up. A lot of customisation can be done with custom css. Try googling css background for example.Catching Elephant is a theme by Andy Taylor
If you choose a different theme all the options in the theme are cleared. Go to Customise > Appearance to upload a picture and fill in any other details again.
The theme I use for Shots is Cargo Theme by Jarred Bishop.