If you are writing tech reports and reviews, you should be able to source appropriate images from the manufacturers. Always worth specifically checking (no harm developing a relationship with their PR department, especially if it means they'll send you press releases direct), but generally speaking manufacturers are not going to cry 'copyright infringement' if you are using promotional product images and specs when reviewing or commenting their products. This is clearly in the realms of fair use and usually encouraged, not frowned upon by the manufacturers.
Originally Posted by ameerulislam
However if you need other images to embellish your blog, you'll need to source them either by creating them yourself, or purchasing them from commercial stock photo sites (you may be able to get some from free stock image sites, or from sites that allow free use with credit). You may also find plenty of people who will be more than happy for you to use their images for no payment, but you have to ask their permission to ensure they are happy for you to use it in the maner you intend.
Not everyone creates to be 'paid' or to earn money, some people simply enjoy creating. Copyright is simply about providing the creator with the exclusive right to decide how their work is exploited by others - it just recognises that you are the owner of the work, no one else. The fact that someone spent time and money creating is irrelevant and certainly doesn't give them the 'right' to earn money from it. But I digress :)
Good luck with your site.