You can display an image in any field by uploading it to the field's description. You can find the option by going to:
Field settings
Standard Options
Description section, upload image icon:
The image will be displayed with the field when the form is filled out:
The total size of images within form descriptions (across all fields!) is currently limited to 1MB. If you exceed this size you will see an error indicating that the form configuration has not been saved.