I asked some friends of mine to upload few pics to an online website with the understanding from the online website that I can always download pics at their original resolution. The pics my friends uploaded were in the 2mb range while the ones I'm downloading are about 300kb. Also, I can judge a slight change in resolution when I zoom in about 6 levels in windows photo editor
As seen in the attached image which shows properties, the original is a 2592x1936 and they automatically modified it to 1536x1147. The website folks claim that since they increased the dpi from 72 to 96, it's the same resolution. Can someone guide me?
What's the question? Yes, they reduced the resolution. DPI is utterly meaningless in this context. What claims does the site make? Obviously they didn't do what you wanted them to do, or what you expected them to do, but did they do what they promised to do per their policies. The business about increasing the dpi sounds like some poorly paid support drone trying to get you to go away.
Mark is correct. FYI, the reason the dpi value is meaningless in this context is because it's just a calculated value based on the number of pixels in the photo and the resolution setting of the monitor on which it is being viewed. If change your monitor resolution to zoom in and make the photo appear larger on your screen, the image will look fuzzy and the dpi value will decrease (pixels are spread out over more of the screen), and vice versa, changing your monitor resolution so everything on your screen appears smaller will increase the calculated dpi value. The image resolution didn't change in this case, only the monitor resolution changed and that changed the calculated dpi value.
The uploaded photo has 2592 X 1936 = 5,018,112 pixels.
The downloaded photo has 1536 X 1147 = 1,761,792 pixels.
These are the only numbers that matter. So like Mark said, the people you talked to are wrong. They decreased the resolution of the photo and the dpi is simply a misleading calculated value. Maybe you could have your friends send you the photo files using Dropbox.com, YouSendIt.com, or a similar site. Many of the photo gallery sites change the resolution, so a file sharing site would be more reliable.