Filepicker Image does not print to page

Hi guys,

I just started using Grav a week ago. I can't seem to be able to get a different images showing for my feature sections. I have a modular page and I'm able to get the "first" image printed from the Page media since I copied this from the Quark template:
{% set feature_image = page.header.feature_image ? page.media[page.header.feature_image] : page.media.images|first %}

And used this in the html:

{% if feature.feature_image %}
     {{ feature_image.cropResize(300,200).html }}
{% endif %}

Here's also the .yml:

.feature_image:
   label: Feature Image
   type: filepicker
   folder: 'self@'
   preview_images: true

I tried to modify the bit I copied from the Quark template but I usually just end up getting some error as a result or it doesn't print to the page at all..

Any tips on how to fix this bit or just do the same thing some other way? Thanks.