Are there copyright issues here?
As PCM posted in the other thread, one can do much better scanning a photo themselves, and saving it in a format that can be printed poster-sized, rather than trying to enlarge these very compressed web formats (jpg and gif).
For instance, I can scan the Greene photo at maximum resolution and save as a bitmap, which makes a file larger than 100mb. Someone needing that kind of resolution for a poster best do it on their own system, if they have the capability.