Here's an example that uses a small X bitmap image in the middle of a sentence. First, at the top of the volume, the bitmap file must be declared as a file entity:
<!entity StopWatch FILE "stopwatch.bm">
Within the help text, the image is inserted using the <graphic> element:
Whenever you see the <graphic entity=StopWatch> symbol, stop and answer the quiz questions.
This markup produces this output.