If you'd like to share a photo or video on Twitter, it must first be uploaded to a third-party website, as Twitter does not currently host any content other than Tweets.

Most of these sites will allow you the option to post your photo or video directly to Twitter, with the option to add a message if you want. Alternately, you can copy and paste their link to your photo or video into your Tweet on Twitter.com. Links to photos and videos from the sites listed here will display your media in Twitter's details pane so that your followers can see your picture or video without leaving their timeline. [1]