Following are some points that should think to use image in Email Template
Avoid background images
Outlook will not recognize background images. Instead, use a background color, and use images in other ways in your email.
Use absolute image paths
If you upload an image to an individual email using the HubSpot image library, this automatically happens for you. If including an image in an email template, host the image on your website. You could upload the image to your HubSpot file manager. Then make your image paths point to the full URL, such as: http://www.yoursite.com/yourimage.jpg.
Correct image HTML: <img src=”http://www.yoursite.com/images/yourimage.jpg”>
Incorrect image HTML: <img src=”/images/yourimage.jpg”>
Declare image width and height
This will ensure that your email design will maintain its structure when images are turned off by email clients.
Use ALT text
Some email clients block images by default, so each image should have compelling ALT text that is compelling.
Optimize image size
Make your image file sizes as small as possible without losing their visual integrity. This will prevent long email load times.
Avoid using PNG images
Lotus Notes does not support PNG image formats. Use a format such as JPG or GIF instead.
Avoid using image maps
Hotmail will not recognize image maps.
Use Gmail and Hotmail glitch fix
When using multiple images, this insline CSS property eliminates a white gap in between adjacent images.
<img src="http://www.yoursite.com/yourimage" width:"10px" height: "10px" style="display:block"> copy right from (http://help.hubspot.com/articles/Best_Practice/email-templates-design-code) :)