Just make sure you right click on the edge not inside the text box of the comment. “You can also display an image inside of a comment. I’ve modified the tip by adding the sentence in blue, with what I think it should say.
The Format Comment … menu choice launches a different set of options dependent on your location in an editable comment. If your cursor is on the text portion of the comment, the context menu operates differently. You need to place your cursor on the highlighted edge of an editable comment before right clicking to launch the context menu. Basically, the general idea is there but a step of magic requires you to know something else. I’d have to say that it did but it didn’t. UDFs differ from VBA macros and you can find my Excel UDF Tutorial here. Updated this post and provided a new blog post that lets you add an image on Excel 2007, Excel 2010, and Excel 2011 with a VBA User-Defined Function (UDF). One of my students noted that a tip in Microsoft Office Excel 2007 Bible (a truly good book on Excel 2007) didn’t provide the magic to insert an image into a cell comment. How you add an image to a comment isn’t exactly what I’d call easy but it is straightforward.