I'm not talking about a New Years resolution, the kind you break a few weeks after you make it. I'm talking about resolution as it applies to images and graphics. Any raster image has resolution. What? What's Raster you say? Well, there's two different types of graphic images, Raster(-based) and Vector(-based).
Let me give you a few examples:
A Vector image is made up from primitives such as points, lines, curves or polygons which are based on mathematical equations. Vector images are very precise and flat.
Raster images are bitmaps. A map of pixels generally formatted into a rectangular grid.
Vector-based graphics are sharp and resolution-independent. So no matter how big you stretch it or blow it up, the resolution will stay the same.
With Raster-based images, the bigger you make it, the more pixels you need so the image doesn't breakdown and become pixellated. (example)
By definition, raster-based files get bigger with the additon of more resolution and vector-based images will stay the same file size always.
When you get a logo done, make sure you get the file in a vector-based format, otherwise it will cost you more to get the file converted to vector, if needed. You can easily convert a vector to raster, but not so easy to convert the other way.
When people take pictures with their digital cameras, the resolution is of vital importance. Many novice users will set their cameras to capture the images in a medium or low resolution setting. This is done to save space since smaller resolution images take up less space and will not fill up a memory card. Sometimes its done because the user is happy with their resolution when they view it on screen and never prints the images.
The important thing about resolution when dealing with a digital camera is that you have a limited opportunity to capture a moment, so you want to get the best image possible. So make sure that the resolution is set as high as the camera allows. You can always down-sample the image later if you want to save it smaller. If you take a small picture from the beginning, you don't have that option.
I can't tell you how many times I get images from people that have been taken off of a web site. The resolution that is found on a web site is 72dpi (dots per inch). Sounds like a lot, but it isn't when you consider that printed media is usually 300dpi. But you say that the image on screen looks just as good as the one on the post card. How could that be? Your eye is much more forgiving of an image that is viewed on a computer screen than on a printed page. As far as the printed image goes, you can get away with 120 or 150dpi just fine, for the most part. But the standard is 300dpi for the best image quality.
So just stretch the image? What? Um, sounds good in theory, but in reality, the quality leaves a lot to be desired. For one, you can't "make-up" pixels. Stretching will just stretch the image and create a pixellated look.
Let me explain it this way; remember when you used to watch TV on a traditional tube? The image was 640 or 800 pixels across. Well now we have HDTV now and if you have watched that in comparison to older TV, you notice how much richer the images are much richer because of the higher resolution. Nobody wants to trade their HDTV in for an old one, its a downgrade. The reason is because that new HDTV offers 1080 pixels across instead of 640 or 800.