These two comptitions are difficult since this type of problem are really rare on Kaggle: the number of landmarks is 15k when a classical competition is about 5k classes and there are an important number of classes with only a few pictures (between 1 and 5 images) with some classes with some substantial number of images.
The write ups about the Kaggle cgdiscount competition shall be useful for the classification one.
Also, the organizers gave a clue: they suggested that the methods to solve the two competitions classification and similarity may help each other…
In fact MS coco 2017 stuff challenge is quite similar and some parts can be used combining with matterport’s Mask-RCNN. But even training coco 2017 stuff may take 2 days or so… So, I think it’s really difficult to test some new ideas. For 15k part I sow some similarity search methods for very large set of classes (I can’t remember for now). Also, RNN and scene descriptions can be used for classification as an idea. My view on this challenge is: time is to short and almost impossible for a single person to do something useful though one can learn a lot but not enough time.