Question: How many pixels do I need for sharing photos online?

Answer: When posting photos online, you do not need nearly as many pixels as you do for printing. This also goes for images that will only be viewed on-screen such as in a slide show or presentation.

Having too many pixels makes it difficult to view photos on a monitor and it makes the file size much larger--something you need to avoid when posting photos on the Web or sending them by email. Remember, not everyone has a high speed Internet connection or a large monitor, so sizing photos down before sharing them is the courteous thing to do. The recipient can always ask for a larger file if they wish to print it--this is always better then sending large files without asking first.

When putting your photos on the Web or sending them by email, the smaller you can get them, the better. There are three things you can do to make your pictures smaller for sharing online:

1. Crop
2. Change pixel dimensions
3. Use compression.

In most cases, you will want to do all three of these things.

Since PPI and DPI are only relevant to print size and quality, when dealing with digital photos for the Web, you need only look at pixel dimensions. Most computers today have a monitor resolution of 1024x768 pixels, so your images should be sized no larger than this for on-screen viewing. Older computers have a lower monitor resolution, usually 800x600, so keep that in mind as well. The smaller the pixel dimensions of an image, the smaller the file size will be.

• When sharing photos online, 800 by 600 pixels is a good average size to go with.
• If you wish to reduce file size even further, reduce your images down to 640 by 480 or even 320 by 240.
• If you're sure your recipients or Web site visitors won't mind waiting a little longer, you may want to go as large as 1024 by 768, but anything larger than that is going to be too large to see in the majority of computer monitors without scrolling.

File compression is another way to make your photos smaller for online use. Most cameras and scanners save in the JPEG format and this format utilizes file compression to keep file size down. Always use the JPEG format for photographic images you will be sharing online. It is a standard file format that any computer can read. JPEG compression can be applied at various levels, with image quality and file size having an inverse relationship. The higher the compression, the smaller the file, and the less quality it will have.

http://graphicssoft.about.com/cs/digitalimaging/f/pixelsonline.htm