The Library of Congress's website states "The Library of Congress generally does not own rights to material in its collections and, therefore, cannot grant or deny permission to publish or otherwise distribute the material."
Therefore, do not use these materials without first checking to see if someone owns the rights in them. Some may be copyrighted and some may not. For example, the Thomas Edison picture you cited appears to be copyrighted: "J259124 U.S. Copyright Office. Copyright by Bachrach." You would need to license rights from the copyright owner before using this work.
The Library of Congress operates a Rights and Restrictions page with information on the ownership of many photos posted on the site. It also operates a helpful question and answer page regarding copyrights in its materials. I've attached the links below.
Bottom line: you assume the risk for using any images. It's your responsibility to research any underlying copyright in the work, if any, before using the photos.
No attorney-client relationship implied or accepted without a signed fee agreement. This response is theoretical only and for purposes of discussion. Attorney is not liable for any opinion expressed herein. Attorney is licensed in Ohio only.
You are right to be concerned . Images that appear on The Library of congress Web-site are not generally available for commercial use. Rather, you must obtain a license from the copyright owner. Some of the images may have been created before 1923, in which event there is a good chance that they are in the public domain. But most of the images are probably still covered by copyrights. You should only use these images if either (a) you obtain a license from the copyright owner, or (b) you obtain legal advice from competent copyright counsel that the image is in the public domain.
You need to read the book "The Public Domain: How to Find & Use Copyright-Free Writings, Music, Art & More" by Stephan Fishman and visit the Internet Archive. See the links below.
The above is general information ONLY and is not legal advice, does not form an attorney-client relationship, and should NOT be relied upon to take or refrain from taking any action. I am not your attorney. You should seek the advice of competent counsel before taking any action related to your inquiry.