Hairspray removes stains from leather but be very careful as it dissolves leather if too much is applied. I find the best way is to spray hairspray into a a container and dip a cotton bud into the hairspray and then apply this to the leather being careful as you go !
Try a 'scuff remover' from a shoe store that is designed to work on leather. Try it on an inconspicuous spot (under the flap, if it has one) first. Apply the scuff remover and buff with a soft cloth or tissue - I've found these to work wonders!
There are also laundry products designed to work on ballpoint ink, but be careful to try them in a hidden spot first.
Try rubbing glycerine into the area and let stand for 15 to 20 minutes.Use dishwashingdetergent and water sparingly.Dab with cool water, dry flat.
There is a chart you can copy off Martha stewarts website with all the stain solutions on it.Good luck!
blotting (never rub!) with alcohol generally works well to remove ink -- rubbing alcohol, not the drinking kind! (That's why people often use hair spray to remove ink stains -- it often contains alcohol.) While it might lesson the stain, on somthing poreous like leather it probably won't remove it completely -- and the alcohol may also lighten the leather. Another option, take the passport holder to a dry cleaner who works with leather and ask if they can provide spot treatment.