There was a thread about posthumous works.
https://www.mobileread.com/forums/sh...ad.php?t=50553
But yes, if the author died in 1949, all their published works are in the public domainin the UK and EU. And I think that, since it's more than 70 years since 1950, a posthumous work published in 1950 is also in the public domain in the UK and EU.
And by the looks of it, covers baseed on unsplash photos are fine.
Feel free to upload to Mobileread.