Keep your photos small, there's no need to upload high definition photos to your blog, the maximum size should be in the range of 800px x 600px, and less than 200k.
You should resize it before you upload the photo to your blog, or a photo hosting site.
...your photos cannot legally be used by anyone else without your permission. Use the information TT has left, and make sure your images have the watermark on them, but also look into putting something on your blog explaining to others what copyright actually means.
The 'Content Theft' link that TT left has some good ideas, but actually knowing the laws of your country / region is always a good idea...
For example, this is the law:
Canadian Copyright Act, 6.:
6. The term for which copyright shall subsist shall, except as otherwise expressly provided by this Act, be the life of the author, the remainder of the calender year in which the author dies, and a period of fifty years following the end of that calendar year.
American Copyright Law
§ 302. (a) In General. — Copyright in a work created on or after January 1, 1978, subsists from its creation and, except as provided by the following subsections, endures for a term consisting of the life of the author and 70 years after the author’s death.
European Union Copyright Law: Directive 2006/116/EC
The Directive (93/98/EEC) harmonizes the terms of protection of copyright and neighbouring rights. The Directive establishes a total harmonization of the period of protection for each type of work and each related right in the Member States – e.g. 70 years after the death of the author for works and 50 years after the event setting the time running for neighbouring rights. Furthermore, it deals with other issues, such as the protection of previously unpublished works, of critical and scientific publications and of photographic works.
This site can help you:
And if you ever find someone using your material online without your permission, you need to know how to file a DMCA notice: