Picture Photo shopping

Hi have 6 photos that i need to be photo shopped. They are to appear on the home page screen of a website. Some of the photos have been edited and have a white background, when these are uploaded to the website they apear with a black background around the picture. The background of the website is blue so the pictures will need to match the sites coulor. If i was to save a picture that is already on the site, then to try and reupload the picture it will apear with a black background. I am unsure of what software the webdesigner used.