The evidentiary bar that the shari’ah has for adultery is so high that it cannot possibly be met unless people voluntarily confess, or deliberately go out of their way to be publicly seen in the act. Four male witnesses of upright character (and no criminal record) must testify under oath that they actually witnessed penetration (which is difficult to actually see). If the witnesses were willingly and deliberately watching (!) they are no longer upright. Film evidence is not permissible as proof because this can be forged.
Even after a confession an adulterer can withdraw their confession and avoid the penalty even if it has already started. This is not a result of un-Islamic legal obfuscation by merciful judges, it is actually the sunnah of the Prophet who repeatedly turned away or tried to deflect people who wanted to confess their sin.
The Prophet said:
Ward off capital and corporal punishment (hadd) as much as you can…
(Tirmidhi; Hakim et al)
Ward off punishments through ambiguities…
I have loosely paraphrased this from A Thinking Person’s Guide to Islam pps 144-147