If you just want some photos for graphics on a web page, there's absolutely no reason to use a high megapixel camera. In fact, you should focus on balancing image quality with image file size. Do you want to keep your web page files reasonably small so that dial-up users don't have a long wait for the page to load? If so, then you want to optimize your web page images. By optimize, I mean strike a balance between image quality and file size. Many websites to a poor job of optimizing images for web use.
I took the photo of the church on this website with a 2MP Fujifilm camera:
http://www.hosanna-lutheran.org/. It's about 45Kbytes but could easily be a smaller file, for a picture that looks exactly the same. In fact, I sent an optimized version of about 30Kbytes to the webmaster but he's being a little hard headed and has not replaced the current one with the smaller file.