From Command-Line Printing in Linux.
N-Up Printing
The -o number-up=value option selects N-Up printing. N-Up printing
places multiple document pages on a single printed page. CUPS supports
1, 2, 4, 6, 9, and 16-Up formats; the default format is 1-Up:
lp -o number-up=1 filename
lp -o number-up=2 filename
lp -o number-up=4 filename
lpr -o number-up=16 filename
The -o number-up-layout=value option chooses the layout of the pages
on each output page:
-o number-up-layout=btlr
Bottom to top, left to right
-o number-up-layout=btrl
Bottom to top, right to left
-o number-up-layout=lrbt
Left to right, bottom to top
-o number-up-layout=lrtb
Left to right, top to bottom (default)
-o number-up-layout=rlbt
Right to left, bottom to top
-o number-up-layout=rltb
Right to left, top to bottom
-o number-up-layout=tblr
Top to bottom, left to right
-o number-up-layout=tbrl
Top to bottom, right to left
So I assume it will be something like this:
lp -o number-up=4 number-up-layout=lrtb -d {printer} {filename} -n {copies}
And it should print 4 images from left to right, top to bottom per page for the amount of {copies}. The numbers you can use seems fixed...
If this does not work please leave a comment.