The approach works well with 200x200 ish images but does get around email software restrictions.
== Method 6 : VML from Outlook ==
Going the way of the dodo, VML or Vector Markup Language [https://en.wikipedia.org/wiki/Vector_Markup_Language Link] is a set of instructions on how the image should be drawn rather than the picture itself. Older versions of Microsoft Office used it heavily when drawing images.
Just because the world is moving to SVG based images doesn't mean this approach doesn't work [https://www.emailonacid.com/blog/article/email-development/emailology_vector_markup_language_and_backgrounds Link]
One of the best solutions for emails is to include tracking data in the email so that sales team can see an email has landed and that a user has read their email.
* Method 1 : works* Method 2 : doesnYou can put tracking into a link the user has to click or if you download an image from a website you can embed the tracking data into the link. User sees an image but it't works report that the image has been requested by a specific user.* Method 3 : doesn't work* Method 4 : works* Method 5 : doesn't work
So there is definitely some thinking to be done on your options.