Flickr is already very popular and most people will have heard of it. As well as the benefits of sharing photos you can use it to help with the start of lessons. In the past I have used the images to introduce a new topic. On the home page of the site, typing in a term like the ‘Sahara’ will bring up all related images. In the top right hand corner there is the option to show it as a slideshow. This saves the time of making up your own image slides and targets those visual learners!
Dumpr was introduced to me by a fellow Geographer. I have been able to use the free tool to change photos into sketches. A much easier way to create a fieldsketch for labelling. There are other free effects on the site including changing images into jigsaws.