I don't know of any image-hosting site that accepts PDFs.
You'll need to rescan it as a jpeg file. (If you no longer have the original picture, and therefore can't rescan, you'll have to display the PDF on your screen and use the Windows Snipping Tool to capture an image of it and then save it as a jpeg file).
You will need a pdf to image or pdf to jpeg converter bednobs. Adobe Acrobat pro is one such way but is not free. I am sure that there are free versions available online. I will have a look around.
^^^ I've never had much success with online file-conversion systems. It still seems easier to me to either rescan the image or to use the Windows Snipping Tool to take a screenshot of it.