Hosting images on subdomain – Error

Hi I’ve tried all day to host my images on a subdomain, it just isn’t working. The only reason I’m doing it is because I’ve been reading that it helps to improve the load speed somewhat (since images are going to be a large part of the site), although i have also read opposing opinions that this method doesn’t really help.

There are no images yet in the blog, So I just followed the steps outlined in many sites and changed
store upload to this folder: /public_html/img
full url path to: subdomain

That just gave me an error:
Unable to create directory /public_html/img. Is its parent directory writable by the server?

I change the permission for public_html/img to 577 temporarily as some suggested, didn’t work.

So I contacted my host and gave them access to my wordpress so they can replicate the error. Everything is fine on the backend. They can’t figure out the problem.

So I poured through more discussion, and changed the path on wordpress to: public_html/img instead of public_html/img (and tried different combinations of no slash and slash)

The error message didn’t show up, but neither does the image. the preview is blank, publishing the post just shows a broken image link, but the image name shows up in the gallery for the post as if it has been uploaded. check the directory shows that no image has been upload

I’m at loss of what to do next. (and wondering if I’m wasting my time and should just go check out CDN instead..) Would appreciate any thoughts or help for this!