We need further context to actually choose the correct word in this scenario. I will add in both possibilities below, and you can use the one that best fits in with the rest of the paragraph. (also, I've done basic grammar corrections, and added a few words to make the sentences more meaningful)
As the process of moulding involves running over the objects extracted from the conveyor belt, the flattening in the tar detected by the computer is not unusual.
As the process of moulding involves running over the objects extracted by the conveyor belt, the flattening in the tar detected by the computer is not unusual.
In sentence 1, the objects have been removed from the conveyor belt. ie. It is their point of origin. They were found on the belt, and were then flattened.
In sentence 2, the objects were removed from another (unnamed) source by the conveyor belt, which then carried them away from the parent, and continued the process of flattening.