All images on the internet are protected by copyright laws, including the ones where you cannot see a copyright notice. This means you cannot use them on your WordPress website without permission.
If the image author specifically states that their photos can be re-used under licenses like creative commons, then you must add a photo credit and provide proper attribution to the original work.
It is really important to give proper image credit to comply with copyright laws and avoid infringing upon someone’s rights.
It is a show of respect for other people’s work and creativity. It also protects you against legal issues and liabilities caused by violating intellectual property rights and copyright laws.