If you can scale your image down the the right size and dimensions, I would recommend simply using the "upload images" feature on E-Junkie that is available at the end of the steps you take to edit your product listing - after you press the "submit" button. Then, you can upload the image to E-Junkie and it will automatically show up at the top of your listing without needing to worry about html coding or hosting the image yourself.
Most of the time that I implement images in E-Junkie shops, I find that this is the best way to do it. You can see an example in any of the shop listings at the link below:
If you really want to host it yourself, I would recommend using any number of free/paid image hosting services that do not use branding - or simply hosting the files on your own website. As for how to code the image, try something like this:
<img src="http://www.YOURIMAGELOCATION.com/images/sample.gif" />
Then, just replace the 'gobbildy-gook' in quotes with the actual URL of your image file as it is hosted on the web.
Finally, you'll need to check the box in the "Required Information" section of the product listing that says "Check this box if you want to treat details as HTML..." And, remember then that you'll need to write your text (including paragraphs and line breaks) by using HTML as well.
If you have more questions about how to do this, or if you need some help implementing it in your E-Junkie shop, please don't hesitate to contact me.