How you go about this will depent on your coding knowledge and the number of images you'd want to show. If you're just using a few, you could have them all in a Menu or Unity UI prefab and show/hide them as necessary using the Menu: Change state Action - leaving the dialogue / speech system alone. Conversations can be built using icons, however, without any problem.
If you want something more complex, such as many images or series of images in a row, you can use custom events to run your own code when AC speech is played. The tutorial I've linked to demonstrates how you can run custom code whenever a line of speech is played - you could do the same thing to e.g. manipulate a Unity UI canvas to show the image(s) you want accordingly.
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How you go about this will depent on your coding knowledge and the number of images you'd want to show. If you're just using a few, you could have them all in a Menu or Unity UI prefab and show/hide them as necessary using the Menu: Change state Action - leaving the dialogue / speech system alone. Conversations can be built using icons, however, without any problem.
If you want something more complex, such as many images or series of images in a row, you can use custom events to run your own code when AC speech is played. The tutorial I've linked to demonstrates how you can run custom code whenever a line of speech is played - you could do the same thing to e.g. manipulate a Unity UI canvas to show the image(s) you want accordingly.