[Koha] Patron Card Images pixelated in PDF

[Prof. Lisandro Laura]

Hi everyone!
I am new with Koha and I have been trying to print decent Patron Cards
but the result is not filling out my expectations.
Patron images and library logo are pixelated despite size, DPI and
format (jpg png).
Patron images on screen are good looking quality, but pixelated when
processing batch in the resulting PDF.
I have been googling around with no luck.
I am running Koha 3.16 over Ubuntu 12.04 LTS (updated the system a few
days ago with apt-get).
The version of Koha is: 3.16.03.000
Ubuntu is 12.04 LTS Server (i386).
About the images, we use several... last attempt was png 200x300px, 300dpi.
We also try 1600x2192px 300dpi with no results.
Is there some fix resolution for images that works?
Any ideas?
Thank you in advance,
Lisandro