You can use the illustrations published on ManyPixels Illustrations Gallery for personal and commercial projects, without the need to include attribution.
The full license
Copyright 2018-2019 ManyPixels
All images, assets and vectors published on ManyPixels Illustrations Gallery can be used for free. You can use them for noncommercial and commercial purposes. You do not need to ask permission from or provide credit to the creator or ManyPixels.
More precisely, ManyPixels grants you an nonexclusive, worldwide copyright license to download, copy, modify, distribute, perform, and use the assets provided from ManyPixels Illustrations Gallery for free, including for commercial purposes, without permission from or attributing the creator or ManyPixels. This license does not include the right to compile assets, vectors or images from ManyPixels to replicate a similar or competing service, in any form or sell the assets in packs. This extends to automated ways to scrape, search or download the assets included on the website without our consent.