I haven't deDRMed the mobi, but I suspect the publisher used undersized images and then they got sized up during the compile process. I've got a couple math books on Amazon.com which make extensive use of images for equations. If you use images that are too small, say 200 pixels wide, they will get resized and start to look pixelated. I find using images that are around 500 px wide keeps this from occuring and the images look clean and sharp in the book--that is assuming they were clean and sharp to begin with. I would not be surprised if the images in this history book were low grade to begin with. Perhaps they were scanned and converted as well as being undersized. At any rate, the publisher should be ashamed of such sloppy work.