Search engines usually does not understand Images with in your websites pages if they are proper or no alt tags for that images..so its better to give alt tags for that Specified Images with the Targeted Keywords. Photo sharing helps you to drive Traffic to your website. You get quality Back link to your website by doing Photo sharing.
Below are the Photo Sharing sites with High Domain Authority and Page Authority:
|S.No||Photo Sharing Sites List||Domain Authority||Page Authority|