At 400 px, they would be too small to print, but you'll still want to protect them as much as possible from being used without permission online. If you remember the Getty/Corbis discussions from a while back on Sitepoint, one of the claims made by the site owners who were targeted by Getty/Corbis was that the companies didn't protect the images with copyright symbols and therefore the website owners felt that they were OK to use. Right or wrong, at this point, I would recommend you don't use high resolution images and you watermark them. You might also consider embedding meta information in the photos as well using Lightroom. There's some talk by the way that Save for the Web strips meta data so consider alternatives.