Is there a free way to prevent those irritating ._ files being generated by OSX?

They are essentially doubles of the files that are already there, and do nothing but take up space on my flashdrive and memory cards.

I've been doing some googling and found software called Blue Harvest that does it, but it'd cost me $120 TT which I'd prefer not spend.

Are there any commands I can enter into Terminal to accomplish the same?