Many people may be unaware that Dreamstime offers free stock photos, in addition to the commercial ones. In some cases they are older or lower quality, but many are there because contributors want to attract people to their portfolio.
This is an example of mine that I donated a while back:
There are some additional limitations on use, but for many these may fit the bill - especially for non-commercial work. I also found it of use when I started out in stock as I could get my hands on top contributors images to get a feel for how their quality was at 100% to see if I was in the ballpark or not quality wise. Handy to avoid rejections on your own work.
You'll also note that contributors get their other images shown next to the free one, so this may provide some additional exposure. You still have to sign up (I think) to get the free images, but there aren't any other charges or commitments...