Pinterest pin it buttons not displaying on images in my photo galleriesi

Hello, I’m having an issue trying to create a gallery where the pinterest pin it buttons will display on the images in my galleries. I’ve tried several gallery plugins and huge it and envira were the 2 that I liked the best cause I could have several columns. But the pinterest pin it buttons on the images aren’t displaying, but are displaying on every other image on my posts. I saw that I could purchase an upgrade from envira to do so but I’m trying to see if there’s a free way to do this. Please help. Thank you.