Not really.

The spoon contained semen at least once, as per the DNA sample analysis.

There is no proof that it is the same spoon as was used in the photographs. They would mention the serial numbers and ballistic tests if that was the case. [detectives say they recovered a blue plastic spoon and an empty container from the trash in Bernd't classroom. - am I to believe that he kept the same items for years, and that he kept them in the trash in his classroom? Did the live cockroaches appear in the classroom too? I suspect they would have triggered an immediate call to an extermination service...]

There is no proof that even if it were the same spoon, it contained semen at the time of the picture. You can use yoghurt in the same spoon before you scoop up semen with it.

There remains also the little problem that feeding them semen would have to be done by osmosis: "who is accused of blindfolding students, putting tape on their mouths and taking photos of them with live cockroaches or a spoon full of semen.". Or could anyone explain how you feed anything to someone whose mouth is taped?

All in all, I see a defensible case, from the defense lawyer point of view. The guy's a scumbag, you'll get no contest from me on that.