Hello,
The way the pictures are aligned can be customized directly from the CSS.
Is this the CSS of the plugin that you are referring to?
You can control their style directly from the css of your website, from style.css.
Please could you tell me what I would be looking for in the theme style.css ?
If you want to center align the picture you need to add in your style.css the following:
div.easy-instagram-thumbnail-wrapper {text-align:center;}
This actually will align all the content to center. If you want just the image to be center aligned but you want to keep the text aligned to left you also need to add:
div.easy-instagram-thumbnail-author, div.easy-instagram-thumbnail-caption, div.easy-instagram-thumbnail-time{
text-align:left;
}