pertaining that you are using royaltyfree/stock images you can upload them without any issues, if the pics belong to someone as mentioned already you would need to get permission to post them publically for people to use, and because they are "generic" doesnt mean that someone doesnt own the rights to them.
most of the time as long as you let the owner of the content know what you are doing with their pics and how you are manipulating them and using them, some dont have issues giving you the ability to do so, if you cant find the author of the originals i would just keep them for personal use.
using other peoples documents/files can be tricky at times, specially when you dont get permission and the original owner finds out, like in my case, i found someone that was using my images as their own on their site and i was pi$$ed, but very confused as to why they didnt ask for permission, i am a simple guy lol and if asked i surely would have said yes to anyone wanting to use my images as there own, but there is nuthin worse then finding your pics with someone elses name beside it on a site....
basically be careful of what your using and always get permission...lol
peas
cityboy