To favorite two (or more) sets of images, you'll login using the same email with a different string.
Here's the example, if my email is example@gmail.com and I need to favorite 3 sets of images then my logins will look like this;
Set One: example+set1@gmail.com
Set Two: example+set2@gmail.com
Set Three: example+set3@gmail.com
And so on, and so on, solely changing the number that follows "set" in an increment of one.
As for everything else, please refer to the selecting images help doc.