I don't get an option to resize my pics, either through FB or my blog (which I now use). If I use my phone in landscape mode then any pic displays correctly, whoever posted it and however it was uploaded
FB automatically resizes pictures unless you turn on upload in HD then I don't know what happens then as I've never turned it on. Don't know about your blog.
Edit: I hate landscape mode but nice tip.
Edit 2: I just went through your posts, your blog images are the size I recommended people resize to so I believe your blog also automatically resizes image.
I do also wonder if the forum auto removes certain sized images after a certain length of time to preserve bandwidth(?) or something
Offsite images don't use any of the forums bandwidth which is presumably why we have to use hosting sites rather than upload directly so I wouldn't expect it removes them.