Erm, I now this is really an Apple issue, not a DT one, but something interesting happens when DT tries to render a PICT - it doesn’t, of course, but thereafter any other image (jpeg, png, etc) gets blurry, requiring a DT quit and reopen to fix.
It isn’t happening over here – .picts individually and in mixed company with .jpgs, .pngs, .tiffs, etc (i.e., in cover flow) render accurately in DEVONthink, and the other image types are not affected by the experience.
Perhaps the fuzzy images have small pixel dimensions and the zoom level is too high. Perhaps clearing the cache will fix the problem. Clearing system caches by doing a safe boot might be helpful.