Hi K_Graham,
Adding a faxcover isn´t very complex. There is a example-faxcover in the hylafax-folder. I ve only edited this one and copy it to a accessible directory for example in the Primaray-Ibay.(\\<serverip>\Primary\fax\deckblatt) Then tell WHFC  (windows-fax-client) the path of the faxcover. Now you can use the faxcover and the adress-data you typed in whfc is printed on the faxcover.
My idea for a background-image is to edit the file ps2fax.gz in the folder /var/spool/hylafax/bin .
I ve edited the end of the file that it looks like:
---------------------------------------------------
...
...
cat cover.ps > temp.ps #write the cover.ps in temp.ps
cat $fil >> temp.ps    #add fax to the end of temp.ps
fil=temp.ps            #set the fax=new ps file
$CAT $fil | $PS -q \   #print the fax
   -sDEVICE=$device \
   -dNOPAUSE \
   -dSAVER=true \
   -sPAPERSITZ=$paper \
   -dFIXEDMEDIA \
   -r$HRES\x$VRES \
   "-sOutputFile=$out" \
    -
rm temp.ps             #remove the temp-file
----------------------------------------------------
With this changes in your ps2fax.gz you can edit the ps-file which will be sent as a fax. The cover.ps is the file for the backgroundimage. You have to copy it to the folder /var/spool/hylafax or where your hylafax-install is. My problem is how to edit the cover.ps that the following data from $fil is printed on the same page. I allways got 2 pages, one for the cover.ps and one for the following faxdata. 
I hope anyone can give me a hint how the cover.ps have to look.
Michael