Here's a list of all the resources that I found in this thread:

Always read, understand, and keep a copy of the license before using any images on your website. Copyright violation can cost you a fortune.

Use Google's advanced search options to find images or videos labeled for reuse.

100 Resources:

Resource List:

Social Media Icons:
- Use only those with Creative Commons License
- Clearly marked licenses such as Creative Commons, or similar.
- Some people found this one to not work well, but others like it.
- READ their terms of use license first.