The transmission case is really too wet with oil to tell where the actual leak is, although it looks like one or two case bolts may be loose. I would check the torque on those oily case bolts right off. Take a rag and dampen it with gasoline and wipe every bit of that leaking oil off the tranny case, the case bolts, and the underside of the car in that area. Then check under the car the next day or so, and see how much new oil has leaked, and from exactly where. The easiest way to see where a leak is coming from is to find the leak when it first starts to show, and not wait until the leaked oil has had a chance to migrate and splash onto other uninvolved parts of the car.
You can never rule out the possibility that a dishonest mechanic loosened a bolt or two, purposefully causing a leak, in order to get your car back in the shop at some later date. It seems very suspicious that you say you had belts replaced and the dealer did not tell you of the oil leaking under your car. I can't believe they would miss that.
It might be that the tranny drain bolt (right between the two bolts full of oil in your photos) is not completely tight, or in need of a new gasket. Unlikely, but easy to check out.
It could also be that a main case gasket is failing, or even a seal (the rear main crank seal is a possibility) or gasket somewhere inside of the tranny has failed, allowing oil to collect on the inside of the transmission case, possibly right above where the oil is leaking out.
There could be quite a few things causing this, but you first want to determine exactly where the oil is getting out, so clean up the case real good, and then keep an eye out for any fresh oil, and try to determine, if possible, the exact point where it is emerging.
If it was the rear main crank seal leaking I'd guess that the oil would be pooling in the lower part of the bell housing. I'd expect the flywheel inspection shield should be just full of leaked oil....motor oil...not gear oil. In fact, try to determine if the leaking oil is motor oil, or gear oil. This should narrow your diagnosis. It looks to have a reddish tinge in your photos. That would make me think it was gear oil. Also, if the tranny is leaking gear oil, it should be obvious if you check the tranny's gear oil level.