I try. For this blog or websites I try to either: create the image (a sketch, as I'm a stinky photographer); find an image in the public domain; or, if those fail and I'm desperate, then I choose one whose re-use isn't forbidden (creative commons licenses get real picky), then, if it seems okay, I credit the image to its creator and link to its source. I figure that's an ad for the original site & artist, but, of course, I'd remove it instantly if asked.
I'm sensitive to the idea of plagiarism, since I've had one architectural design stolen, over the years, and maybe-possibly-65%? of a design for a musical. So I try to be careful about copyright.
A public domain photo I'd used, um, wasn't. Luckily, I figured that out and could track its photographer. Tara Bradford was very kind and allowed me to use the image after all. Check out her blog or her website. Gorgeous photos. Tempting to steal more of them! But don't.
ADDENDUM: I have permission from photographer Tara Bradford to use this photo. But it's STILL copyrighted!
DO NOT Pin this image or copy it or any o' that stuff without her permission. If you're looking for a cute alphabet, look HERE instead.
ADDENDUM: Go ahead and check out that site, but the photo has been replaced there by my own sketch. Just simpler.