This is a static image field that forms a cosmetic component of the template. It can be used for including the corporate logo, or any other image, as part of the template. This field is set by the Logo view of the Inspector. Images may have these file name extensions and formats: PNG, GIF, JPG, JPEG.

When the Logo icon is dragged into the Workspace, the Logo object looks like this:
With the Logo object still selected, drag or Set an Image file (see the Inspector explanations above) and the Logo object will be replaced with the selected image:

Print Template Variant
A variation on the Logo Properties Inspector view occurs in the case of the Print Template which has the vernier Adjustment, % tool included:

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Transaction Template - Topics of Interest