There are plenty of options available for image hosting indeed. Some recommend the official Trainz Gallery - and someone who uses it could give you better directions on that - but Imgur.com seems to be one of the best external image hosters out there at the moment. It is free, easy to use, and has no risk of suddenly disappearing and dying like Hostthenpost thanks to its highly active community (in which participating is purely optional). Flickr is also another good option but it's more of a real gallery site than an image hoster.
Cheers,
SM