For non regular gamblers are gambling losses deductible against gambling winnings up to gambling winnings?

For non regular gamblers are gambling losses deductible against gambling winnings up to gambling winnings? Do the gambling losses have to be in the same year as the winnings?
Is there a point to hang on to old lotto tickets? 

Do either copies or scan's of losing lotto tickets suffice should one need to later use to deduct against gambling winnings?