Possibly the font?

I realize that you put the text on the book pages, but if that was someone else's book, the text is their copyright. Isn't there some process that took the place of a note to the reviewer where you contact support to explain? Or you could submit a property release for the book (as the creator of it) which would probably also make them happy.

Can't tell anything  about the isolation issues from a reduced version, but try selecting a white area in the background with a 0 tolerance on the magic wand. If you have all sorts of areas not selected ('cause they're not white), that will need to be cleaned up.

it's the STABILO highlighter, i even got vectors rejected for the protected shape.

Besides that,  i guess the isolation is not done very well

Hold on, is it me or is the paper on the right white, and the paper on the left blue?

Totally agree with what everyone is saying - not a great presentation for many reasons...
But it's also poor execution of a concept.
If it's a book on learning Spanish why isn't there a translation of the words not just words repeated in Spanish?

Indeed, that's very odd, and what would the highlighter be for?

BTW, I thought the OP had done a bad job of removing the writing/branding on the pen rather than the pen being grubby, but in any case, as said above, the pen shape is probably copyright and the font may also be.

Marker - logo and writing still visible.



After that, the other advise isn't why the image was rejected, but could be next time.