When you add a question to a quiz, you are not actually adding the question but rather a pointer to the question that resides in the question bank. For your problem, it would be useful, although a bit laborious, to add the same description question to
each new page. Unfortunately, Moodle does not allow you to add the same question more than once in a given quiz. And it wouldn't be very convenient to duplicate the description question as many times as you have pages in the quiz just so you
can display them.
A workaround is to put the long description including the graphic in a block. In the HTML code of the block, place <div id="description" style="width:100%;"> at the beginning of the description and </div> at the end, and add the following
In the block configuration and under "Where this block appears", set "Display on page types" to "Attempt quiz page". In the quiz settings and under "Appearance / Show more...", set "Show blocks during quiz attempts" to "Yes".
This way, the long description including the graphic will appear at the top of every quiz attempt page.