Resolve "RGAA 4: implementation 1.2.1"

Closes #489 (closed)

see: rgaav4#20

example: https://www.teclib-edition.com/en/about-teclib-open-source-editor/

• NMI ---> without decorative image marker
• Failed + NMI ---> with decorative image marker (class="vc_single_image-img")