I would like to know if it would be consided a violation to use an image with a standard licence as a thumnail for a youtube video. The image would not feature in the actual video itself. Please advise
Probably not. But I would strongly recommend reading the licensing terms.
Look here for more information on licensing: https://community.adobe.com/t5/stock/links-for-licensing-terms/td-p/11366788
(Disclaimer: As always with licensing, this is my interpretation of the rules. I think they are correct and advice is based on reading and interpreting the licence terms and on fair use for both the buyer and the artist/stock company, but I cannot rule out that my interpretation is wrong. I'm not an Adobe employee).
Thank you for taking the time to reply