When you get "full sized" images from others, it's because it's simply a link to a file hosted on some server, much the same as a web page.
All of which is beside the point, since email was designed for TEXT ONLY. If you want to include an image, do so as an attachment. If you want to include all kinds of cutesy graphics and fonts, get a free bit of space on some free website place and create a web page instead. Then just send people a link to that page.
Email servers are already clogged with all the spam people send out either intentionally, because they're using programs like Outlook and Outlook Express which have been compromised, they were using Internet Explorer and some malware set up a SMTP relay, or they were just running their own open relay. Please show some consideration for everyone else on the Internet with you, and try to keep the traffic where it belongs. Web servers tend to be run on much more powerful systems, often times clusters of systems, which are designed to handle heavy traffic loads. Email servers generally are run on considerably less, because email generally doesn't require that much. Of course this means they can be overloaded much more easily if people insist on trying to send large attachments and bloat the message size considerably by adding in font effects like colors, bold, italic, etc. Those all more than double the size of any message.