What is the ruling on ridiculing studying and diligent students, and the ruling on pictures that may mock supplication, and the ruling on celebrations after exams?

It appears that the questioner is suffering from obsessive doubts (waswasah) regarding disbelief (kufr), and succumbing to such doubts leads one into confusion and pathological skepticism. As for the mockery mentioned, it does not lead to disbelief unless the person intentionally meant to mock and belittle the religion or disparage it. What occurs in jokes might be mockery of the study method or administrative dealings. The scholars have stated that disbelief does not befall someone who commits an act that could be interpreted as apostasy or otherwise. Scholars have also mentioned that if there are ninety-nine reasons pointing to the excommunication of a Muslim, and one reason to keep him within Islam, then the mufti and judge should act upon that one reason. Whoever's faith is established with certainty, it is not removed by doubt; rather, it is only removed after establishing proof and dispelling ambiguity.