Viewing images

[junderw2]

Why do some images on my computer (photos) appear really grainy and blurred while other images open ok ?

[wildwood]

Most images on the web are stored with a minimum acceptable resolution (number of dpi - dots per inch) to save memory space. Really sharp images are quite memory intensive.
It may be that you have the program that you are using to view the images set to 'fit image to window' in which case your computer stretches the image to fill the program's window and causing it to become blurry.
You can experiment a bit by using a small sharp image and, using a photo editor program, enlarge it to whatever size you wish. That should make it appear a bit more grainy. Unfortunately, making a large blurry image smaller in this way does not usually make it sharper, just jagged.