Does imagining forbidden images constitute lowering the gaze, or does it invalidate the repentance of lowering the gaze, and is invalidating repentance a sin that necessitates new repentance?

Imagining forbidden images does not make the imaginer guilty of looking at them, nor does it invalidate repentance; due to the Hadith: "Indeed, Allah has pardoned for my Ummah whatever evil thoughts whisper in their hearts, as long as they do not act upon it or speak about it." However, one should not dwell excessively on such imaginings.

If repentance is invalidated, this is a sin that necessitates a new repentance. Repentance has three conditions: acknowledging the sin, regretting it, and resolving not to return to it. If the rights of created beings are involved, then returning those rights or seeking forgiveness from their owners is also required. And Allah is Oft-Forgiving, Most Merciful.