The action that would be considered a violation of the Creative Commons BY-ND license is:
photoshopping a house into the photograph
This violates the license because the BY-ND (Attribution-NoDerivs) license specifically prohibits any modifications to the original photograph. The other actions mentioned (putting the image on a flyer with attribution, uploading to a personal web page with attribution, and sharing on social media with thanks to the photographer) comply with the license as long as proper attribution is given and no modifications are made.