How to handle Backup Images in HTML5 banner ads. ProblemI have been given specs to build banners for Tubemogul / Adobe CC, and I am unclear on how backup images should be handled.This has caused some confusion with developers, traffickers and producers, with no clear answer.BackgroundI build my HTML5 banners from scratch (No Adobe Animate, or GWD). That said, there is no clear guide on what to do for any platform.After looking through the ad specs link below:Ad Specs and Guidelines I found this guide document: Dropbox - HTML5 Zip Container Walkthrough.pdf Media agencies, and clients have sent me several versions of the above PDF, which annoyingly has code snippets AS AN IMAGE, and sometimes has working links and sometimes it doesn't. However, the most frustrating part is the one on backup images which reads:Caveat: Fallback images are not supported when using Ad Cloud to serve HTML5 display creatives. To implement fallback images, you need to build them directly into your HTML5 creative according to the HTML5 browser support matrix.N