That's a security measure implemented in the software itself to prevent uploading malicious files to the server, the extension must match the file type, if you open the image in text editor you can see the file type in the first line.
I never open a notepad++. This avatar file was uploaded in 2008 JPG. I saved my many folders of anime 1995 to 2015 50.000x total file.
I opened notepad++ on this .JPG original, and doesn't have remote or no any problem. Just a word there,
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OiCCPPhotoshop ICC profile xÚSgTSé=÷ÞôBKˆ€”KoR RB‹€‘&*! Jˆ!¡ÙQÁEEÈ ˆŽŽ€ŒQ,Š
PNG and photoshop ICC profile. I guess that is old 2008 date time. Who made that picture was a DeviantArt original. I uploaded to my own site was works fine. And JAF site too.