Copyright Photos

I like others on here like to sometimes add a photo to my work, I know it does not improve the content of a poem but maybe helps with the imagery. I do avoid using pictures that are watermarked or where permission is required or even those that say this image maybe subject to copy write. But I couldn't help thinking that maybe we could be on dodgy ground. I would gladly put the photographers name against it if I knew who had taken the picture. The last thing I would do is 'steal' someone else's work. I have no problem if someone wanted to use one of my poems as long as they leave my name against it and not try and claim it as theirs. Does anyone have an understanding about what we can or can't use. Also does anyone know if its possible to put your own photos against your work as when I've tried to do it a red X comes up but that does not happen when copying the image url off the internet.