You are perfectly right, I have tested yesterday with a small (20 pages) PDF in image format, with pages a little bigger then the size of the Cybook screen and they showed as white pages when I tried to read them.
It looks as if the Cybook does not like images much, and PDF image files at all at this moment - one can always hope that future versions of the PDF reader in the Cybook will be much better dealing with this situation.
To get something readable now, several things are involved.
First, one as to convert the image PDF’s into text PDF’s.
To do that a OCR program as to be used. Omnipage Pro and Finereader Pro (this one costs in my country around 1/3 less) are the software kings and can OCR PDF’s directly.
Then a text (txt, word) file is created, it then must be “proof read” - this is what takes more time and costs more money in building a digital library environment, and I really must stress it’s the biggest cost involved - to correct OCR recognizing and formatting errors.
Finaly it’s the building the final eBook.
If you have Adobe Acrobat there is a quick and dirty way - use the internal OCR from it.
I advise the use of version 8 as it’s OCR is generations better and more accurate then the one in older versions of Acrobat.
So OCR the PDF’s you have in Acrobat choosing the option for “formatted text and graphics” in PDF Output Style.
Then import the obtained PDF file in Mobipocket Creator, who will create a Mobipocket eBook (prc file) not perfect but quite readable.
This procedure does not give you the problems with the correct size for the screen of the Cybook one as with PDF files.
I hope this is of some help.