Most email marketing software solutions will provide wizards for the design of emails. They will suggest arrangements of text and images which will be perfectly adequate. But you should want more. Wizards are there for guidance and should not be seen as prescriptive.

You will be given options for the location of a picture but the choice of image will be down to you. Remember that it is not there merely to add a bit of colour to the page. That could be done in other ways. Nor is it there just to look pretty. It has a role, a function that it must perform.
The overriding purpose of the email is to get the recipient to do something, perhaps click through to a landing page, subscribe to your newsletter or maybe just to be aware of your presence. Everything else, if indeed there is anything else, should be subservient to this prime function. So you should judge your image on this factor only. Everything else is fluff.
The main danger to all emails, once opened, is the ease at which it can be deleted. Most people know the keyboard short cut so keeping them reading has to be the major consideration. Pictures can be paramount in this.
Readers of emails do not, despite the description, read them. They scan. They will do this in the preview pane and the email proper. Glorious prose with careful scene setting and a gradual build up toward the dénouement is of no use. It must be a blitz, straight between the eyes.
Your logo is an important reassurance to the reader that he knows the source of the email. But it will be subliminal, hardly worthy of the word glance. The subject line of the email would have prepared the reader for the heading. The next bit is all important.
The fact that they opened the email suggests that they have some interest, or even just a hope, regarding what the email is all about. Their eyes would have gone over the logo and heading with the briefest of pauses before falling on the picture.
There are limitations on your choice of image. It must be:

• Relevant,
• Simple enough to grab the attention instantly,
• Exciting for the reader.

Relevant: if your clientele is sophisticated then a picture of the Taj Mahal supporting a holiday in Mumbai might inspire them to read something else. Any non sequester will grate.
Simple: a reader will glance at it before moving on so it needs to be capable of being understood in an instant. Too much detail means that it will be ignored.
Anticipation: the picture should not be an end in itself. It must hint at something so that the reader will want to know what comes next. It should lead onto the text.
The choice of image is a critical one. Don’t just go for one that looks attractive to you. Consider its function. It needs to engage the reader and in an instant.