There is currently no way to disable it. May I ask why you don't like the one with the poster art? 
Is this the one you prefer? 
Here is more information about this featureļ¼
https://forum.dvdfab.cn/forum/dvdfab...nfo-system-faq
Mona
Hi Mona, every rip I have ever done using DVDFab is stored on a external hard drive.
The thumbnails have always been square, some with poster art and some without. It was just the other day that I noticed that the final rips are now in portrait, which makes them stand apart from the rest of my collection.
I'm not complaining, it looks good. Just different is all.