What is the legal ruling concerning someone who prolonged looking at a pornographic image during the daytime in the days of Dhul-Hijjah, without ejaculating or releasing anything, and does this invalidate his fast?

Gazing at what is forbidden to gaze upon is unlawful for both the fasting and the non-fasting person. However, it is more emphatic and the sin is graver for the fasting person. The fast remains valid, and whoever commits this must perform sincere repentance.