Just remember not to take offense if we ask a follow-up question (even if it sounds dumb or noob-ish). This forum has the entire range of users, so anything is possible. I wasn't asking to belittle you...it was just to knock out the easy solution so if that wasn't it...we could move on to others.
Going by what you said, it definitely sounds like something is causing the photo to show in "actual pixels" as opposed to sized appropriately for your screen. Again, I'm just guessing here, but are you using the latest video
drivers? If so, check to see if your computer is set to think there's a second display....maybe the photo is being stretched out across your display, as if you were extending your desktop. Some laptops have hotkeys for this, others have it in their video
driver settings.