How to Change Terminal Background Image on Ubuntu 18.04?

Sadly, that option no longer exists. See bug 698544 :

• Comment 1 (2013-04-22) is Christian Persch's (rather incomplete) answer to the bug report.

  Do not.

• Allan Day 's comment 45 ( 2013-05-13) provides more details.

  I've spoken to Christian and he gave me the background on this issue.

  The ability to set background transparency has been removed as part of a larger cleanup of the gnome-terminal codebase. This kind of modern work is very much needed, and it should be remembered that the terminal has an ancient and complex code base. Background transparency is also known to cause a range of performance issues, including slowness and memory leaks.

  Considering the number of active end developers, the need to clean up the codebase, and known bugs with background transparency, it was decided that there were no resources available to maintain background transparency and keep the quality at the desired level.

  We understand that some users are disappointed by the disappearance of this feature and hope they understand that this decision was made to make other improvements to the terminal code that will lead to other improvements in the long run.

  While Christian's initial response could have been better, he has responded in detail via private mail, and I suspect he's just tired of the question.

_{*Bold is mine.}

_{**This answer makes Persch sound like a jerk, but that's not my intention. Read Day's last sentence for context.}