Maryland state law allows speed cameras in work zones and in school zones. The law requires that you be allowed a 12-mph tolerance and there must be a "conspicuous" sign for a work zone that's photo-enforced.
I don't know whether there are any work zones right now on either I-81 or I-68, but the easiest thing to do is just to make sure you don't go 12 mph over the speed limit in any work zone in Maryland. Err on the slower side in case your speedometer is slightly off (also, I don't trust them to calibrate the cameras correctly).