Anything within the Public folder you can right click and choose copy public link to get a URL to the raw image. The format of the URL is such that people can't look at it and figure out the URL's of other files in the same folder as they look semi randomised.
There are a ton of different image sharing sites but one reason I use Dropbox apart from already having an account is that I can easily upload photos taken on my iPhone or iPad to Dropbox directly from the device for later linking within a post.
The image of the connector I took with an iPad, used an app called iResize to scale it down to 800 wide, then uploaded it with the Dropbox app, then later linked to it while writing the actual post on a PC. Much faster than using my point and shoot, transferring to a PC by cable, scaling, uploading etc, and the camera of an iPad 3 is more than good enough if there is enough light.