The color profile on your image may be set to CMYK. CMYK is used by the graphics industry to print full-color on a physical medium.
Most web browsers won’t display images with a CMYK profile properly. Your image will need to be converted to RGB.
Photoscape is a good program with which to do this. Go to http://photoscape.org/ps/main/download.php and download the program. Make sure to click one of the download links in the middle of the page and not the one at the top.
Photoscape will only save images as RGB. Opening your image with Photoscape, then doing a Save As, and selecting .jpg as your format, will convert your image from CMYK to RGB.