Many internet service providers offer (or USED to) a free personal website for each account. They don't give you a ton of disk space, but if you trim your photos down to a reasonable size for internet posts (not full size as they come out of your camera) then you can put a lot of them up on your personal website. I never used the personal websites that my ISP's have provided, so I don't know how easy they are to use. But if your ISP provides that, and you can figure out how to work it, that would be a free way of hosting your pictures.

These free ISP-hosted websites are not meant for heavy-duty hosting. I think your ISP would get mad if you posted pictures that were getting ten's of thousands of hits per hour. But that shouldn't be the case for pictures on a forum like ETS.

Another alternative might be the third party hosting site postimg.org. I have never used that site, but in a different forum that I frequent someone asked a question just like yours in this post we're reading now, and that website was suggested.

Also, note that maybe forum websites (but not ETS unfortunately) provide a way for you to upload your pictures directly to the forum website in your post, negating the need for a third party hosting service. Look for something in the thread creation dialog box about "uploading" something, rather than "linking" something.