No, you don't have to be subscribed!
JOSH authored a good tutorial in ANNOUNCEMENTS but I couldn't find it on the quick search. Maybe you or someone else can find it again...
Basically, use an off-site image hosting site like Flickr, Photobucket, etc. Upload your images to that site, copy the code from the 4 choices of 'share this photo', paste that code into your post on THP where you want it (relevant to text in the post if such correlation is important), Submit Post and it's all good!
Those who choose to get an Extreme membership have the option of uploading directly to the post, no need for the off-site host. That's a perk, but there are TONS who use (and have used) Photobucket or whatever for quite a number of pics for years. I have 4 years worth of TDs and Drunken Chef-ing posted up using Photobucket. :D