In perfect copyright / plagiarism issue..... it normally is not okay to grab a picture from Google. But to be fair... I have done it 2-3 times. It can come back to bite you. If you use a photo that belongs to someone else. And later they do a search and see you used it... and see your post paid out $50 or $100. They can make a fair and legal claim for all or a portion of that reward. Or simply sue you for using it. This normally only happens if you are successful or make money off the blog(which at steemit, we do) but they are legally capable of suing just for using their image without asking. Each time and always that you can use pixabay.com or another free image site... that is 110% better and safer! IF you do otherwise.... do so with caution and restraint.
Amongst Steemit and Steemians... It seems to be allowed that you use others' photos as long as your post is the MEAT and the image is just the garnish. IF the image you borrow really "Carries" your post, then not really okay.
I see, another great and helpful comment, thank you.