If you write a blog post, it is likely protected by copyright law. Copyright protection gives the author of a work the exclusive right to make copies of that work and to distribute copies of it without permission from the copyright holder.
The copyright holder can license this right to others, but generally cannot prohibit others from making copies or distributing them.
If you write a blog post for personal use, you may not be infringing on anyone’s copyright. However, if you write a blog post for commercial purposes (including, but not limited to, generating income from the blog post or from advertising on the blog), you may be infringing on someone’s copyright.
If you are unsure whether your blog post is protected by copyright, consult an attorney.
Ultimately, whether or not your blog post is copyrighted will depend on the specific facts of your case. If you are in doubt about whether your blog post is protected by copyright law, consult an attorney.