This would have been easier to answer had you mentioned more about what kind of "works" these are.
If these were works by Rembrandt, I would say image fits best. People gaze at images with their eyes, so image works best for sculptures and paintings.
If these were works by Huxley, I think portrayals would be a better word. As your defintion states, portrayal can be defined as "a word picture," so portrayal is a better word for descriptions written on a page.
Technically, representation is defined as an image or likeness of something, but it's often used to described copies, not originals. Given your context, I think it could be safely removed from consideration.
Since Bohumil Hrabal is an author, portrayals would be the better word. However, you've only asked about three words, and I'm telling you which of those three would be better. Yet there are other words that probably deserve consideration as well, such as:
Characterizations of women in Bohumil Hrabal's works.
Descriptions of women in Bohumil Hrabal's works.
However, I'm in no position to tell you which word is best, because I'm not really sure about the details of what you'll be studying.