I have found that PIC Monkey is the best editor that I have found thus far. You can crop, correct exposure and color, add a watermark, and so much more. There is a free version, which has many options to choose from. You can also upgrade to use their special fonts, collage frame, etc. 
When posting photos to your blog or website you want them to look professional as this is a representation of your company. As they say a picture is worth a 1,000 words!
- Always crop your photos so your background does not distract from your image.
- If you don’t want someone taking your photo as his or her own, add a watermark.
- Enhancing the color and exposure to your photo will bring out the intricate details.
- For an event create a collage. This will allow you to showcase several photos at once. Hence keeping the visitor engages with your message a little longer.
- The last tip is have fun with it and you will be pleased when you see the results.
Here is the link to PIC Monkey: http://www.picmonkey.com/.