Even 10 years ago most emails were picture-less---all text. Now pictures are expected and a whole lot of text is a sure way to be ignored. And before posting pictures to a website, blog, or email running through a photo editor can ensure your pictures won't be ignored too.
One of the best free editors available is Photoscape from Photoscape.org This editor allows you to re-size, brighten, sharpen, and apply additional contrast to your photos all in one batch which can be a great help making your work more efficient.
The main way to improve most photo's is to brighten and adjust the contrast. And remember that photos posted should be at a size less than 1000 pixels for efficient loading. I've been to some blogs where the photos posted took so long to load that I left before looking at the content. If you take the time to put up the content be sure to make it viewable.
And when taking product pictures be sure to get in close to your subject. A photo taken close, in good, natural light will shine and attract a lot of attention.