Thanks for the replies, dear people..! :)

Dear Niko, the crops you see here are actualy 1:1 scaled ones...
I mean, they are cropped directly from the approx. 2700x2100 pix master image which is the scan of the printed 18x24 cm photo at 300 ppi.
I may post you the master image as a 256 bit greyscale JPG image (JPG conversion performed in ACDSee 3.0, and at 100% quality - least compression). I do not know the exact data load of such a file, but I think it will be around 1 MB maximum.
If you say OK, I'll be dealing with this after work this afternoon, but I may need your e-mail adress...
Any suggestion from you about compression..?

I'm thankful for all the interest... :)