How do I replace a bullet with an image?

You're on the right path...the autonumbering is how to do this, but you can't directly place graphic into the autonumbering properties.

Here's what I use in my FrameMaker - Working with Content reference book

The pencil icon is from the free (and amazing) web font called FontAwesome. By applying a character tag to the autonumber specifying this font I can specify any of thousands of icons from FontAwesome and adjust size and color as needed.

The icons even have 4 different styles per icon.

Students in my online Template Workshop learn to create this example, and they also get a copy of my template file to use as a starting point for their own work. All formatting is provided via a paragraph tag called N-Note, and thus I can quickly apply this format to any paragraph in my project.

I can also quickly work up other formats, and here are some examples from my template file.

-Matt

That's because if you want to use an image, you'll have to add each one an as inline image, and that's a lot of work.

Any chance you can use a font with box and a checkmark? A capital R in Wingdings 2, for example.

~Barb