No. This follows from the Berne Convention, which is the basis for copyright legislation in all civilized countries in the world and also in in the USA. It stipulates that all creative works become subject to copyright as soon as they are created:
The enjoyment and the exercise of these rights shall not be subject to any formality (Berne Convention, Article 5(2)).
The images you talk about are there automatically subject to copyright, and according to copyright law, you need permission from the copyright holder for any use that is regulated by copyright, including the uses you ask about.
None of the thing you mention (the non-commercial nature of the project, giving attribution, etc.) impact on the images' copyright status. If it is copyrighted, it is illegal to use without permission from the copyright holder.
What happens if latter the e-book is made commercial?
Using images without permission gives the copyright holder the right to sue you and demand compensation, even for non-commercial use. The amount courts will give the copyright holder usually depends on two things: Commercial use and attribution. Both commercial use and lack of attribution results in the offender having to pay more in compensation.
Obiter dictum: I am fully aware that it is not unusual to re-use images without permission and without proper attribution on the Internet. Most copyright holders probably never know that their copyright is breached, and a lot of them doesn't care anyway. So the probability that you are going to get sued for pasting images "found" on the Internet into an e-book is not high. But even if you're not caught, you are still breaking the law.