Is what is discharged from the male organ upon viewing provocative images and pictures of foreign female artists considered maniyy (seminal fluid), and is it permissible to perform tahara (purification) daily as a precaution, especially since I always pray in the mosque?

Viewing forbidden images is impermissible and exposes one to the wrath of Allah. Allah Almighty is aware of what His servant does, and one must repent of this sin. The mentioned discharge from the questioner is most likely madhy, which necessitates ablution (wudu') but not a full bath (ghusl (definition)), and its purification method is clear. As for maniyy (semen), it necessitates ghusl. If a person is unsure whether the discharge is madhy or maniyy, then according to the Shafi'i school, they may choose between the two.