Sharing my solution for adding an image to your Submission Form email notification.
For this to work, you need 2 deployed DataPages, 1 Submission Form and 1 Report DataPage both using the same table containing the image path as DataSource. Copy the code below inside the message body of your email notification and don't forget to click "Source" before inserting the code.
<img src="[@cbBridgeServer!]/dpImages.aspx?appkey=InsertYourDeployedReportDatapageAppkeyHere&file=[@field:YourImageFieldName]" />
http://howto.caspio.com/files-and-images/referencing-your-files/
Cheers!