A file that's the right size to deliver a high-quality print is definitely the wrong size to post on the Web or send via e-mail. A 3,000 x 2,000-pixel JPEG image, for instance, may be about 3MB. If you print it at 300 dots per inch, you'll get a nice 254mm-wide print. But if you send it via e-mail, the recipient will have to view it in an image-editing application to be able to see the entire image on even the largest monitor. To spare your audience some grief, select Image > Resize > Image Size and change the width to, say, 600 pixels (with Constrain Proportions checked, the height automatically changes to 400 pixels, retaining the original's width/height ratio). Rename the new image so that the original is still available for archiving and printing.

Unless you resize images meant for printing, e-mail recipients will have to open an
image-editing app to see more of this handsome iguana than its eyeball.

The resized image will now be possible to view, and the file size is probably less than one-tenth of the original's. To reduce the file size even further, select File > Save For Web. You'll see two side-by-side images, with the original on the left. Set the quality to zero and note the file size shown below the image. If the image quality is not acceptable, move the quality slider gradually to the right until it is. When you reach an acceptable setting, the file size will still be lower than before, and your recipients will still be your friends.