Editing images using the Web
There’s no need to grapple with an expensive program like Photoshop, but you do have to learn how to edit photos. Digital cameras these day routinely take 4-, 6-, or 8-megapixel photos, which translate into multi-megabyte files. These files are too big to email to people who just want to see your holiday snaps, so you need to at least learn to crop photos and change their resolution.
Resolution is how many pixels your photo contains, and the area they’re spread over; it’s measured in dots (dpi) or pixels (ppi) per inch, depanding on whether the photos are printed or just displayed ona a screen. First, you need to know how many pixels your photo currently contains–you can use Get Info or Properties to find its dimensions. Most computer screens are not much more than 1000 pixels across, so that’s as big as you need for PowerPoint or a web page. If you’re submitting a picture for publication, an ordinary journal prints photos at only about 250 dots per inch: estimate how many inches wide your photo will be printed, multiply that by 250, and that’s the number of pixels you need. If you want to know more about resolution, dpi, ppi, try this simple explanation, or this more detailed one which includes a discussion of those mysterious megapixels.
To edit a photo to a better size, and crop it down to the relevant parts, you could always get a photo-editing application like Photoshop Elements, Paint Shop Pro, or GIMP. But sometimes you’ll need to resize photos on a public computer cluster or while travelling. The best solution then is to use any one of the following web-based photo editors, all of which I like.