Find a kiosk that does the 8x10 insta prints, vs the developed ones behind the counter...
It's been awhile since I did 8x10s, but I did re-reprint some clearly pro shot Senior Class photos at Target of my girlfriends son, we had paid for and had a release waiver from the studio, but the 18 year old girl behind the counter didn't even flinch or asked to see it...
Honestly you will hear it all the time, small talk or befriend the person behind the counter at a box store like Target and you will likely slide by just fine in many cases...
And who is to say you don't have (hint hint) a reprint release form from that stock photo image collection company you downloaded it from?