1. Test uploading different types of image files (like .jpg, .png, .gif, .bmp, etc) and see if you could upload them.
2. Test uploading other files (like .exe, .dll, .mpg, .mov, .mp3, .wav, .rm, .doc etc) and see if It could break the uploading process.
3. Test with an image file with size other than the specified limit (the maximum allowed size was 500KB. So I had to try with 0 KB files, 1 MB image files, 5 MB files etc).
4. Try uploading a virus infected image file [You can use EICAR (European Institute of Computer Anti-virus Research) test files. These files are not actually viruses but behave as virus files] and see if the web server could detect the virus and stop the upload!
5. Test typing in a wrong path (like typing 'F:\ walpapers\aamir_khan_001.jpg', in place of a correct path 'F:\ wallpapers\aamir_khan_001.jpg'). Look at the wrong spelling of 'walpaper'). This can easily happen if a user is entering the path of the image file to be uploaded instead of browsing and selecting the image file. I had to see that the system was capable of detecting the wrong path name of the file.
6. Test cancelling an upload process and see what happens.
7. Test with a slower network speed and low system configuration.
8. Test While unplugging the internet connection while uploading.
9. Rename a images file with special characters and test by uploading it.
10. Test with corrupted image files (wrongly encrypted files).
11. Test by changing the file extension in browse field after selecting one image.
for Ex : Chnage jpeg into GIF
12. Test By closing the browser while uploading
Link for downloading virus affected files : http://www.eicar.org/anti_virus_test_file.htm