I use imageshack, it's free, unlimited and comes with a handy little uploader program - simply start it up and either drag and drop the image in to the uploader or browse for it, select the size that you want and upload. Then another little screen (below) pops up with a choice of formats for copying elsewhere - I use the direct link - just copy and paste that line into your 'enter image url' box and Bob's your Uncle.
I imagine the other programs work similarly.