don’t want to can’t be an MVP anymore” Sewell may have swallowed the blue pill (or was it the red pill?) but he still produces occasional nuggets of wisdom.
According to Scott, if you need to extract a background image or a custom element from an existing Power BI file, make a backup of the file, then rename the backup’s file extension from .pbix to .zip and extract the contents. The background files are stored as gifs or jpgs or whatever they were uploaded as. You’ll find them under the \Report\StaticResources\RegisteredResources folder within the zip. (And don’t get me started on whether it’s pronounced “gif” or “jif” – because I (Scott, that is – t.j.) prefer “jeef”…)
If you don’t have the report in Power BI Desktop format, you can export the report from the Power BI service.