There's a couple ways to get higher quality stock photos legally and for free:
1.) BigStockPhoto - they are running a 7 day free trial where you can download up to 5 images per day at any resolution and in any format. You just need to enter in a valid credit card (which they will process a test transaction of $1, which will later be refunded). The only catches are that you need to cancel the trial on like the 5th or 6th day at the latest, because they try to bill you for the full month before your trial is up. Also, make sure you do not accidentally click *any* buttons that mention anything about "upgrading" your account or anything like that - it will instantly end your trial and instantly bill you, without even a confirmation page. One other thing to look out for, is make sure you select the proper file size and format before downloading - by default it points you to a rasterized copy at a medium resolution. So if you, perhaps needed an EPS file instead, you have to waste another one of your downloads to get it if you screwed up the first time. They only allow one offer per email/credit card. Technically speaking, if you have a few credit cards and some extra email accounts, you can take advantage of this offer several times. Or just pick up a temporary credit card at the drug store for like $3. Not entirely free, but still, $3 for several hundred dollars worth of free stock photos is still a deal.
3.) DepositPhotos - If you sign up through one of their affiliates (append "/stockphotosecrets" to their Domain for one of them, sorry I cant post URLs right now) you will get 5 free credits. These are enough for one medium sized photo of your choice. You can keep logging out and signing up again to get more free images. They don't even check to see if any of your information is valid, so you can enter all bogus info.