The quickest way to get an image uploaded and obtain a URL for the custom background of your Landing Page is to use google drive.
1. Open drive.google.com
2.Click New -> File Upload
3. Upload your file to wherever you want in drive.
4. Find your file in the list. Right click it, and select 'Share.'
6. In the following popup, click the 'Get Shareable Link' link on the upper right.
7. Then, click on the drop-down menu above the generated link, and select 'More...'
8. Select 'Public' and then click save.
9. Click Done.
10. Right click your file again , and select 'Get Shareable Link.'
11. A new popup opens below the file, and the link should have auto-copied.
You can press ctrl + C ( cmd + C on a Mac) if you're not sure that it did.
12. Paste this link into a new tab. Do not go to the link just paste it in, because we are going to edit it first.
13. In the URL, replace the word 'open' with 'uc.'
14. Now, you can press enter and visit that link. The link will change and become much longer. Save this link to use it in your landing page.