how do i make an Images that do not convey meaning a artifact? I have to have a document 508 compliant and this is what I received back...

Document(s) does not have alternative text for image(s) that are meaningful. Alternative text descriptions communicate the meaning of content relevant images to users of assistive technologies and text-only browsers. When images do not contain meaningful and informative alternative text, the image's purpose and function is not conveyed to the user. Alternative text should provide sufficient information for understanding of the content when the image is removed. Images that do not convey meaning or that are for decorative purposes should be marked as artifacts.