The matter is that no Outlook desktop version supports the background images because of the background-image style applied for pics displaying in stripe, structure or container. This style is not supported by the Outlook email client.
Let's look at the example where we added the background image to the structure. Here is a screenshot from the editor mode.
Now, let's check how the same email looks in Outlook.
As we can see, the background image is missing in Outlook.
As an option, we can add the Outlook-friendly background image to the whole email template.
Go to the "Appearance" → "General Settings" tab, enable the "Background image" control, and upload your image.
In this case, a hidden comment is applied in the program code, and it only works with Outlook; it allows users to see a background image.
By the way, as another option, you can add an additional background color to the container, structure, and stripe in the editor.
These colors will be visible in Outlook, and in the other ESP, there will be a background image.
Here is an example of how the background color could be added to the structure.
This is our result in Outlook, the background color is visible instead of the image.
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