This follows on from the earlier post on Creative Commons.
Use this feature on their website to search the internet for images and files you can use in your blog.
You can search for a variety of things and select whether you want to use them for commercial reasons or whether you want to be able to ‘modify, adapt or build upon’ them.
This is a comprehensive resource however the results you find are not likely to display accreditation information clearly so you will have to check the terms and conditions on each individual website.