Where do MTG spoilers come from and why are the images low quality?
Most spoilers coming directly from Wizards, or other authorized spoilers we get nice full sized images that are clear and easy to read. But occasionally we get spoilers taken from promotional items Wizards sends out. In this case the spoiler image was scanned or photographed from a calendar of events that Wizards provides for stores to put up and have the time and format of their FNMs, Pre-Releases, etc. The Mastadon is the promo for the release events and for that date it has a picture next to the date. As you can see here it is fairly small, about half the size of a normal card. That is why this one is such low quality.

The other main reason that spoilers from Wizards are low quality is that they spoiled them at a Con and the only images we have are ones people at the con took with their phones. For example when Crux of Fate was first spoiled the only pictures we had were from people that attended PAXAus, it wasn't until later that Wizards gave us higher quality images.