The Facebook grid tip is a good one, Canva is also a good (pretty inexpensive - images are free or $1 an image I believe) tool to grab an image you can edit / layer text on top of for things like social media posts / blog headers (they have "Facebook" specific sizing and its built to be editable by non-designers):

https://www.canva.com/

And there's a good list of similar tools here:

https://blog.bufferapp.com/tools-create-images-for-social-media