OK, have managed to reach a solution to this issue regarding getting images load so thought I’d leave an explanation as to what was required.
I was unable to get external images embedded into the email when adding the following to config.php
But… I was able to get images uploaded to the phplist images folder/subfolder ( shown as images/image in example below) to work when I included all of the following to config.php:
define( 'EMBEDUPLOADIMAGES' , true);
define('MIMETYPES_FILE', 'mime.types'); - For this to work I had to create a mime.types file that included all MIME file types I was looking to upload/use & place in root (public_html) directory
Once I’d added all the above to the config.php file, created the mime.types file and was careful to not go over the total attachment files limit of 100kb (not sure if it’s possible to change this limit - is it?) then the images were embedded into the email & so were dispayed on all emails sent out - nice one, looking great.
Thanks to @duncanc & @Dragonrider for helping me along the way.