[kaerast]

On some badly configured Nginx servers the filename extension isn't parsed correctly. A php.jpg file will be executed as php because a badly written regex will match the .php.

Even if you don't have such vulnerabilities you probably don't want people to be able to upload images to your server. They could easily send you over quota on shared hosting and use your bandwidth for serving their own images (including child porn).

[teyc]

Yup. That would be my worst fears.