Scan it, bring it into photoshop, see what its like as a bitmap if no good desaturate or greyscale, adjust curves in photoshop so its a black n white image, slight gaussian blur, then sharpen to take away any scan defects - see what its like as a bitmap again. If no good import into corel, do a trace, under bitmaps tab, see what results are like - if ok delete background and convert any of the image to 100% black. Print posi - all text/images have to be black to make a posi. simples.
Every image is different so some need further steps - some don't need all or any of the above, its trail and error.
Cheers John