Replacing bars with objects
A second type of chartjunk is obtained by replacing the rectangular bars in a barchart with pictures of objects. This a much more serious problem since it often visually mis-represents the proportions in the different categories. Are the values proportional to the heights of the objects, their areas on the paper or their 3-dimensional volumes? At a quick glance, most readers would use something between area and volume though it is usually the heights of the bars that actually determine the size of the objects in this type of diagram.
Recreational participation in New Zealand
The diagram below was published to show the percentage of men and women participating in various recreational activities in 1996,
Again, the visual impression is misleading because the widths of the carrots also change. In particular, the employees getting under 5% merit increase seem visually unimportant, but they comprise nearly 10% of the total employees.
If you are determined to use pictures...
Pictures in bar charts are really chartjunk and should be avoided — they do not make the information in the data clearer and have the potential to mislead. However if you are determined to use them, it is much less misleading to use stacks of pictures that are all of the same size.
Example
The bar chart below might be used to represent some aspect of car ownership or accidents.
Simple bars would be clearer, but the 'ink' used in each stack of cars is roughly proportional to the group's value, so the diagram does not badly mislead.