Can I use someone else App Design Screenshots for preview purpose for my app landing page?

Hi, I am planning to make an App Landing Page but I don’t have any app design that I can use for preview purposes in my landing page. So can I use someone else app design just for preview purposes?

If you know any site where I can get screenshots for preview purposes only then please share a link or something, Thank you

You can only use another persons work if it has the right license or their permission.

Will you not need an app design to make the landing page for it? Is that not quite an important component of the item and design?

Thanks for the answer, let me see if I can manage any app screenshot for preview purposes.