I took a lot of time to research an answer for this one. What I have learned. Passed is a past tense verb, in your example I believe it would be relating to "he" as the none its describing, he moves passed the camera. Past, in this case, would be an adverb describing the word "speeds", speeds past cameras. Personally I don't understand the details enough to say that one is right and the other is wrong, were it me from what I have learned I would say that the first one would be right, if I had to choose one. Like I said, I'm not sure enough to say if one or both are right. That said, here is the link where I learned the most about this. http://www.dailywritingtips.com/passed-vs-past/ I never thought I would learn so much about the differences between passed and past. Though my answer was inconclusive I hope it was helpful to someone.

'Past' is correct. You speed past (beyond) something. 'Past' is a preposition. Once you speed past the camera, you have passed it it. 'Passed' is the past tense of 'pass' and not a preposition.

Nope, neither. They are "speed cameras". If you call them "speeding cameras", then you mean "cameras which are speeding". A speeding camera would race you down the street... but these don't exist (yet). You wouldn't use "passed" in this case - it has a passive meaning here, so it means a (speeding) camera which has been passed (ie. overtaken). Not only is this already a strange image, but you've also broken the sentence. "He speeds" is intransitive, so you need a preposition (such as "past") to follow it. Lastly, as Jeff rightly pointed out, repeating words is redundant, so it's better to use "traffic camera". "He deliberately conceals his number plate whenever he speeds past traffic cameras."

The second sentence is ok but speeds and speeding are redundant and can be confusing. There are no speeding cameras. I could interpret this sentence as the person concealed his plate as he was racing a speeding camera. An improvement would be: "He deliberately conceals his number plate whenever he speeds past a traffic camera." Traffic or Road camera is a better description of what he sped past.