Should text files or image files be virus scanned during upload?

I have created an online web app for my company. It's being tested for security files. The tester loaded the EICAR text file. The virus scanner on the server caught and removed the file.

I have only allowed text, gif, jpg and pdf files for upload. How likely can a text file, image file have a virus? I know things changed a lot lately. We are on Windows 7. My question is, is there even a need to run a virus scanner for such file types? Thanks.