As a blogger, you may want to use a photo in your post to emphasize your subject. For stock photos, you can buy from iStockPhoto or Fotolia, as low as $1.
If you don't want to pay for it, there are also some places to find free stock photos. Here I recommend FreePixels, it has over 3,000 photos/images in 37 categories. You may find some useful photos for free...