The best case is to produce your own photographs. Of course, not even professional photographers have a stock of every kind of photograph one could want to use, so there are other ways to license use of someone else's photo;

1. ASK. Sometimes it's as simple as sending the original artist an email saying "Can I use your picture of ... for ..." Sometimes the answer will be yes, other times it may be yes with conditions, rarely they will say no.

1. BUY STOCK. When you buy the rights to a stock image, you are paying the artist for the right to use that image.

2. USE CC0 or other "free" stock from pixabay.com or another stock photo site that licenses images for commercial use.

NOTE: Using an image on a Steemit blog is COMMERCIAL FOR PROFIT USE. This means you MUST have permission to use the image for commercial purposes to avoid copyright claims.