When I post photos, I shrink them to 800X600 pixels, which is still fairly large. I have a 17" monitor and I have my screen resolution set at 1028X1284 pixels(or something like that). The photos fit easily on my screen, and I haven't been taking smaller screens or bigger resolutions into account when I size them. I have a feeling that's where your problem lies.
BTW, I shrink them to 800X600 from 2048X1638. Be glad I don't try to post them that size!
DB's right; it's a chore and a bore, but I do it, too. Posting photos is very tedious and time consuming, but I enjoy sharing the photos so I don't mind the effort.