When using images from the internet for your blog, you must get the necessary permissions to use that images. When someone uploads an image to the internet that he owns, that person remains the owner of the image. Whether or not you can use it depends on how the image is uploaded.
When you Google Search for an image of a dog, and click the image icon, the search results are all the images, the ones you can use for your blog, and the ones you can’t use. When you click the “Tools” icon, what remains are the images that you can use. You cannot use the images that are not in these results, unless you get permission from the owner. The results are divided into two categories: “Creative Commons Licenses” and “Commercial and Other Licenses”. Creative Commons, is a blanket permission to everyone, that you can use the image with attribution or a link to its source. You must go the the website source of Commercial and Other Licenses and see what their terms are. Sometimes they want payment.
Pixabay is a site where images, other than the sponsored image on the top, are free to use without attribution..
Pexels is also a place to get images where permissions are not necessary.
When using the photos from Flickr, you must look into the permissions of each individual images. The permissions link is on the bottom right hand side. Public Domain images do not need a link to its source, but you might want to do it as a courtesy.
You can’t use images from Facebook, Instragram and other social media without permission either. On any website, look for permissions. Be careful. There are firms or individuals out there who sue firms or individuals using their images without permission.