Thanks for writing back Pulkit, but I'm still unable to get through the URL personalization. Here's some more detail on what it's like.
1. In the Email Designer, I drag-dropped an image element inside of a structure component. In its source, which is plain HTML with some custom attributes for ACS integration (such as data-nl-expr etc.), I can't find a way to paste the URL from my custom resource, the path of which looks like so - /context/targetData/cusRPNA_TSMovieslink12/movieImageUrl. Embedding it into the src attribute of the <img> tag doesn't work.
2. At the pane to the right, I tried enabling personalization, which provides a new attribute in the source of my image element which being data-nl-imgep-perso-attr-src. This attribute allows me to use the poster image URL from my custom resource by pasting down the path (/context/targetData/cusRPNA_TSMovieslink12/movieImageUrl). While this sounds convincing, the image still doesn't load in my mail as seen in the inbox.
The data contained within /context/targetData/cusRPNA_TSMovieslink12/movieImageUrl would look like this - https://creativenerds.co.uk/wp-content/uploads/2017/01/godzilla.jpg for instance.