While all photos on Pexels are free to use, you are not allowed to sell the photos as they are without making significant creative changes and adding unique value to the image so that it becomes your own work.
This means you cannot simply apply a filter, change the color of the image, crop it, or add simple photo enhancements and then sell the photo.
Some examples of what you could do to significantly alter the image to make it your own would be:
- Adding artistic typography and/or other graphic elements to the images
- Using an element of a Pexels image in a collage
- Using an element of a Pexels image as a background for your own content