In order to Doodle on pictures, users simply choose a picture to upload, then hit the edit button and choose the Doodle tab. It's possible to customise the Doodle by changing the colour and pen size, and you can draw or write on pictures. This can be used to draw attention to different parts of picture, or simply send a message.
According to Mary Meeker's annual Internet Trends report, Internet users around the world are sharing nearly 2 billion pictures with each other every day through various photo sharing platforms such as Facebook, Instagram, WhatsApp, Snapchat and others. Facebook already owns Instagram and WhatsApp, and together, these three services account for the vast majority of pictures shared. Through this move, Facebook is hoping to take on Snapchat by adding to its photo sharing capabilities in the hope of tying in more users to the service. The feature has already rolled out to Facebook's Android and iOS apps.
Facebook has been bringing Snapchat-like photo editing features to its apps and Web service for a while now. Facebook introduced the sticker feature to its mobile apps back in February, and by June, it began rolling out an updated version of the feature, complete with photo filters and text. In August, it allowed users to add filters, stickers, and texts to their Facebook photos right from the Web interface.