How to fix

• Option #1: 
  • "Content" pane
    • View > Show/Hide > Navigation Panes > Content > right click on the contents that you want mark as an artifact and select "Create artifact"
• Option #2: 
  • "Reading Order" pane: 
    • Tools > Accessibility > Reading order > Show reading order > Review the reading order (You can review your content by selecting "Page content order" or by "Structure types") > select the content that requires tagging > Chose the type of tag > OK
• Option #3: 
  • Tools > Accessibility > Set Alternative text > Checkmark "Decorative Figure" for the image that is selected.
• Option #4: 
  • "Tags" pane:
    • Options > Tag Annotations (This option will allow Adobe Acrobat to auto tag all the annotations in the document)

Screenshots

Option #1

Option #2

Select your element that you'd like to tag as a background/artifact and choose "Background/Artifact" from the reading order dialog box.

Note: This is simply an example of selecting an element (logo in this case) and tagging it as a background image. It does not mean that it is mandatory to tag your logo as an artifact or background image. 

Option #3

Option #4