With Astah, you can add images which are associated with models stereotype. For example, when you want to show Database icon on UseCase diagram, this is how you do so.
(4) Another dialog appears. In the stereotype field, enter a stereotype in it and then click [Icon] button and specify the image file you want to associate with model which has this stereotype. In this example, I type “database” and upload an image of database.
Then the model will turn into the image uploaded!
Give it a try!