Images

All images here are stores as losslessly compressed PNG images, in order to avoid comparison-distorting additional artifacts by JPEG compression.

User-friendly scanning methods

Here are images, using the scanner's default settings and comfortable tools with an easy-to-use graphical user interface:
Scanned using the web-interface of the 6310 with default settings (there are no resolution/quality options):

It might look "ok", but if you zoom in you can clearly see the ugly JPEG compression artifacts. This is a no-go for scanning raw-material to be in a print later.
Scanned using Kooka (KDE). Again default JPEG-compression settings of the scanner, but this time with 300 dpi:

Again the JPEG compression, but the resolution is way better.
Again this scan comes from Kooka, but it seems that the scanner is outputting ugly interlaced-looking stuff with some resolutions. In this case, 250dpi (instead of the above 300dpi) leads to stripes in the image.

The raw image produced by the scanner looks like that. I don't think it's Kooka's fault.

"scanimage" commandline tool

300dpi scan with JPEG compression still enabled, but compression set to 0 (=best), using the jpeg-quality option:
scanimage --jpeg-quality=0 --resolution=300 -d hpaio:/net/Officejet_6300_series?ip=192.168.x.x > imagefile.jpg 		300dpi lossless and compression free TIFF:
scanimage --compression=None --format=tiff --resolution=300 -d hpaio:/net/Officejet_6300_series?ip=192.168.1.51 > imagefile.tif