Could you tell me, if I find something that I like on Shutterstock and I decide to modify if it or create something similar and use that with my own commercial product, could be I punished or face legal liability for that? I don't want to recreate a virtually identical thing. I won't use colors, I want to use shape only. I appreciate your answers.
I am not an attorney. This answer does not provide any legal advice, other than to advise you not to rely on legal advice from strangers on the Internet, and to consult an attorney in your jurisdiction for actual legal advice.
TL;DR: It depends on how much your work is transformative from the original. You will probably not find a clear answer, until after you made your work and either were sued, or nobody noticed or didn't care enough to sue. Making your work for commercial purposes makes it harder for your work to be considered transformative (that is, not liable for copyright violation).
Note: this answer refers to US law.
You are talking about (hopefully) creating a derivative work,
an expressive creation that includes major copyright-protected elements of an original, previously created first work (the underlying work).
While the linked-to Wikipedia article deals primarily with US copyright issues, it also includes some reference to international law, such as the Berne Convention for the Protection of Literary and Artistic Works.
Basically, for your work to be considered a derivative work, is has to be substantially transformative, different enough that the "reasonable person" would consider it a new work of art worthy of its own copyright, rather than mostly the same as the original work with some mostly inconsequential changes. If your work is not transformative enough, it would be considered a violation of the copyright of the original work.
It is not at all clear what constitutes "transformative enough". It is determined on a case-by-case basis, guided by previous court case law where types of transformations have been ruled on.
Because you want to use work for a commercial product, you probably can't fall back on fair use of a copyrighted work if your image is not transformative enough to be a derivative work. It's possible — one such fair use is parody — but if you're using it just to sell a product, or for product packaging, that probably won't work.
Shepard Fairey, who created the famous Barack Obama "Hope" poster, was sued by the Associated Press for unauthorized use of a photo by AP freelance photographer Mannie Garcia. It is not clear whether Fairey's poster is transformative and therefore derivative, or whether it was in violation of AP's copyright — the case was settled out of court for undisclosed terms.
Perfect 10 was an adult entertainment magazine that had a subscription-only website with images behind a paywall. Several websites copied the images and placed them on their own sites, which were then later indexed and cached by Google, making them visible and findable with a Google Image Search.
The US Ninth Circuit Court found Google not guilty of secondary copyright liability, because Google's use was at least partly transformative. The court also commented on, but did not specifically consider the weight of, the fact that Google's Image Search provides a public good, and that public good might make up for lack of enough other claims, such as fair use, if the work isn't transformative enough:
we must weigh Google’s superseding and commercial uses of thumbnail images against Google’s significant transformative use, as well as the extent to which Google’s search engine promotes the purposes of copyright and serves the interests of the public.
... the district court did not expressly consider whether this value outweighed the significance of Google’s superseding use or the commercial nature of Google’s use.
... We conclude that the significantly transformative nature of Google’s search engine, particularly in light of its public benefit, outweighs Google’s superseding and commercial uses of the thumbnails in this case. … We are also mindful of the Supreme Court’s direction that “the more transformative the new work, the less will be the significance of other factors, like commercialism, that may weigh against a finding of fair use.”