Don't know about the dpi issuse, getting back to the uncomplicated
thing, here is how Print Screen can be used.
Screen Capture ( make sure you select jpeg, anything else is a bigger
size )
If you are in any windows based program, just hit the Print Screen key
on your keyboard ( or Ctrl + V ) and you have a full screenshot.
If you hold down the 'Alt' key with the Print Screen key, you will
capture only the window that is on your screen, not the whole desk top.
This sends it to Clipboard, now you can Paste it into Paint ( go to
Edit ) or any other Windows based graphics program.
Save as...
Save as type, select JPEG etc.
If you need to crop it, put it in any Edit program and crop.
I use Screenshot Captor myself because it has all I need for cropping
built in, text comments, arrows etc.
http://www.donationcoder.com/Software/Mouser/screenshotcaptor/
Less complicated & better than Print Screen, because it will produce a
screenshot in one action, as against two by Print Screen, is Gadwin.
Gadwin PrintScreen
http://www.gadwin.com/printscreen/?prnscr
Windows 98/Me/2000/XP, or Windows NT 4.0SP6
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Screenshot Pilot free
http://www.colorpilot.com/price.html