I know that most people here have a good handle on what they're doing, but I've always found it useful to read another person's take on a subject, especially if I thought I knew all about it. Amazing how much we know for a fact that just ain't so. ;-)
So, in the spirit of General Clarification and Debunking of Common Nonsense, I offer this link. I think the website is very useful - clears up misconceptions, and the writing is a model of clarity.
Re image size and resolution -- some comments based on my experience:
a) Keep archival originals of all photos - work only on copies.
b) Web posting and e-mailing: change image size by changing the pixel dimensions.
c) Resolution has no effect on image file size - it does have an effect on the printed image. Generally speaking, leave the resolution as is. Your software and the printer driver will produce a good image.
d) Image size and printing: You may have to reduce an image in order to make importing it into your word proc program easier (or even possible.) If so, make sure the imported image is large enough that you have to reduce it to fit. If you have to enlarge it, you'll get the jaggies for sure. Ugly. Also use the corner handle to change image size, else you'll end up with bloated or squished faces. If you want images to fit a column, resize all to the same width (say 2400 by whatever). Do any cropping _before_ you resize.
Bottom line: photograph at the highest size your camera permits, resize images for mail or web posting, and for printing only if necessary.
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