When you scan, you can choose an option for the image size, either by pixels, or inches (or mm). Quality size (dpi or number of pixels) can vary from around 72 dpi (low quality) to very large. Even though 72 dpi is low for printing it usually is good enough for viewing on the internet. Another tip is that you can save the image as different file types. Most common for internet use are *.jpg or *.gif. My scanner will only produce *.tif files so I must convert them to one of the other two in a seperate program. Usually whatever you use to view the images will allow you the "Save As" option where you can choose to save as a jpg or gif. *.tif files are larger than *.gif or *.jpg in file size. If you want to email me the images, I can work on them and post them for you. Then we'll know for sure what is happening.
Best of luck,