Size and Sharpen Photos
Whenever you want to use a photograph for something, you always have to size it. Even when using film, you had to make a print sized specifically for the need or use of the photograph. With film, you simply put the negative into an enlarger and make the picture bigger or smaller as needed. Digital is a little harder because you have to be very specific in how you create a size for the image. Things like resolution and physical size must be treated separately.
In general, do all of your processing work on a photograph using a master Photoshop, or PSD (Photoshop Document), file, and then save that master file for any future resizing purposes. Create a new file for every major change in size of picture you need. ...