Images in the handbook

I believe the recommended resolution is "if it looks okay." ;-) (Though that standard isn't always followed…) Something to consider is that many of the images are of necessity screenshots of dialog windows and things like that, and it's not possible to improve their resolution beyond the display of the screen they came from. MuseScore's Image Capture by default produces much higher resolution images than a regular 100%-scale screenshot, so the images on the Shared Noteheads page are of fine quality.

EDIT: Actually, they may be too large now. I see you replaced them since yesterday. The way it works is, if they're larger than the width of the page they're automatically scaled down to fit, but there's no limit to how tall they can be. The new images are the same resolution as the old ones, I gather, but not as wide—and so they're considerably bigger in the Handbook.