Adobe Illustrator

• Vector Graphic Images - shapes created using paths instead of pixels
• All fonts should be converted to outlines
• Embed any linked files, but also provide the support file separately
• Illustrator can also create very complex vector images that may end up being separated in Photoshop

Thanks Threadless and artist Rosemary 
Traval for this perfect example of vector art
for screen print - TARDamask 

 Thanks Sharp Shirter for the excellent vector
example - Cycling Fish

Adobe Photoshop

• Raster Images - design elements created using pixels instead of paths
• Best for very complex graphics or photographic images
• Images be created at a minimum of 150 dpi at print size
• Up-sampling web images does not make the graphic use-able for screen print
  
  

Thanks Sharp Shirter for letting us use Venn
Jelly as an example!