Rule one: think about the purpose of your image.

1. To explain a concept?

2. To link an idea to a visual clue?

3. To assist with an explanation or navigation?

4. To engage learners?

5. Something else?

Rule two: consider consistency and clarity

1. Concept: does the image really help explain a concept? Does it make sense? is it easy to follow/read?

2. Is the image a diagram, photo?

3. Does it have text/legends and if so, are the words visible? 

4. Are you linking several ideas to several visual clues so do you need a consistent look and feel?

5. Do you want the images a similar size - e.g. icons should be the same size. Others may vary.

6. Do you want a consistent colour scheme?