Your Gmail inbox is functional, but it’s a little plain.
It’s simple to spruce it up by adding a personal photo. Start by selecting Settings in your Gmail inbox and choose Themes.
You’ll be offered a wide variety of themes to choose from, scroll down to Custom Themes where you can choose between a light or a dark theme.
You’ll be asked to select a background photo. You can choose from featured photos, your own Google + photos uploaded from your phone, a URL or you can upload the photo of your choice. Most of your photo is going to be covered up by the photo, so choose something that looks nice with just the edges showing. Pictures with a landscape orientation look best.
As you can see from the photo below, you only see parts of the photo. You’ll probably want to experiment with different images and see what works best.