Thanks for the useful advices (I did write quite much here recently but still consider me as "new")!
What is still not clear for me is how to use images one found in the Internet. Is it "allowed" to include them in ones texts (or only to give the link to the page?) as long as one adds the original link or what exactly is to be done?
I have been using images from places like WIkimedia where the licence allows re-use, but I also link back to where they came from. I think that's okay. You can use the Tools > Usage Rights options in Google to find such images. I try to use my own images when possible, but it does help to have some image on a post to get people to notice it in the feeds.
I've not had anyone say I'm doing it wrong so far.