hi anna,
i have done the related test in excel 2013 and 2016 on windows 10, pictures could be inserted into comments in the same way. you may follow steps and check the outcome.
1.right click a cell and select insert comment.
2.select the margin of the comment and right click it as shown below>choose format comment. note: don't select the content of the comments, or you can only see font in the format comment.
3.click colors and lines> expand color>select fill effects.
4.under picture, click select picture to insert pictures.
if that couldn't help, you may try running the online repair and check the outcome.
moreover, since the issue is related to the excel usability, we suggest you post a new thread on
excel it pro discussions in technet for better assistance.
thanks for your understanding.
felix