This is a little tutorial on getting the HP OfficeJet Pro 6869 to work, including printing and scanning.  Please note that I'm using Linux Mint 18, "Sarah", Cinnamon edition.

What you need to have is HPLIP version 3.16.3 installed.  This will easily recognize and set up the printer for you, though it will recognize the printer as the 6960, instead of the 6968.  Also, it will use the driver for the 6830.  For scanning features, we're going to have to do a little more work.

First of all, the libsane-hpaio package has to be installed.  Usually, this is installed by defaul.  Second, we need to change some configurations.  Look to the /usr/share/hplip/data/models/models.dat file for the configurations.

Just so that we don't mess up the configuration file and bork our install, let's back up the file.  Just type in this command as root from the command line:

#cp /usr/share/hplip/data/models/models.dat /usr/share/hplip/data/models/models.dat.backup

Now let's open it up in gedit.  Since this is a root-owned file, we'll run the program as root.  I'm using the Cinnamon desktop, so I press Ctrl+F2 to launch the run command dialog and type in gksu gedit /usr/share/hplip/data/models/models.dat.

After opening up gedit as root, scroll down to the entry for officejet_pro_6830 (you can use Ctrl+F to quickly find it).  Underneath this entry, copy and paste this:

[OfficeJet_Pro_6960]
align-type=-1
clean-type=-1
color-cal-type=0
copy-type=0
embedded-server-type=1
fax-type=6
fw-download=False
icon=default_printer.png
io-mfp-mode=1
io-mode=1
io-support=14
job-storage=0
linefeed-cal-type=0
model1=HP OfficeJet Pro 6960 e-All-in-one
model2=HP OfficeJet Pro 6968 e-All-in-one
monitor-type=0
panel-check-type=0
pcard-type=2
plugin=0
plugin-reason=0
power-settings=0
pq-diag-type=0
r-type=0
scan-src=3
scan-type=7
status-battery-check=0
status-dynamic-counters=0
status-type=10
support-released=True
support-subtype=447b
support-type=2
support-ver=3.14.10
tech-class=CopperheadXLP
tech-subclass=Normal
tech-type=2
usb-pid=7212
usb-vid=3f0
wifi-config=3

These are the same entries for the HP OfficeJet Pro 6830, however it works just fine for the HP OfficeJet Pro 6869.  Once you've edited that, save and close the file.

Now when you power on the device, SANE should be able to recognize it.  To test it out, launch xsane (if you have it installed).  If the scanner was properly set up, the program should load and should look like this:

After that, you should be able to scan pictures to your heart's content.