Sorry. False alarm.
After tinkering some more, I eventually noticed the problem was occurring during transfer since I could view the image locally. I then tried using my webhost's cheesy FTP tool and viola, the file was uploaded successfully. I have used the ftp function from the DOS command line for ages so I'm not sure what's messed up now...unless the default file type got switched from 'bin'. Actually, I'll bet that's the problem.