I tend to agree with much of what your blog outlines. I think pages of learning with visuals that are there ‘just’ to enhance the look and feel of a course can add value to the experience and just generally make it a nicer place to be and learn in. I dislike the cheesy stock imagery ‘Man on phone, looking surprised’ or ‘Team of young professionals walking triumphantly from a business meeting all high fiving’ but I think stock libraries can often provide alternative, less obvious choices with a little imagination.
Generally speaking, I think imagery for mobile which is overly detailed for the smaller screen size or which has too much going on is annoying/distracting, as is overkill on the ‘wallpaper’ stock library stuff. On mobile devices I think striking the right balance between reducing noise and distraction but maintaining richness and engagement with fewer but ‘better’ images is the way to go - bold, clean, clutter free images that speak to the target audience and all supported by icons would be my choice (and everything optimised for a user downloading over a 3G connection).
Video obviously also plays a part, but in my opinion it does depend on connectivity and nature of content.
Be good to hear what any art directors/graphics folk have to say on the subject.