I get that there are operational costs, that much is obvious.
But the cameras are cheap, and there are enough opportunities to have cameras pointed at bikes by people (or fixed), whether dedicated to that purpose or not that I can’t see budget being a major factor, especially when it is so important to the sport.
I know thermal imaging is not that accurate, and alone could never been used as concrete proof, but used in conjunction with other technologies as a a warning/flagging system to highlight bikes for further checks it could work well, which is why I’m surprised it hasn’t been used more widely.
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As a side thought, given the disparity between UCI and team budgets that you highlight, and given how massively important it is to the sport to be doing something about it (and be seen to be), and how important it is to the teams to have a clean rep and also to out other teams who might be cheating, I wonder if either some sort of levy/investigation tax on the teams would ever be feasible, ie: make them pay for the resource to investigate.
It would be a brave team indeed if one of them would turn round and say, here you go, we believe this is so important to the sport, here is £XXXX we are putting forward to help fund impartial investigation.
</daydreaming mode>