List values within your installation may have been configured such that there is an image associated with each value in the list.
For example, you might have a list of countries, and there may be an image of the flag for each country stored. When this field is chosen for a report, there is an option to display either the title only, the image only or both the title and the image associated with the title. To select these options for a report, right-click on the button by the selected field and view a dialog that will look like this:
When images are included in reports, they may look like this: