The Recent Post widget that wordpress.com offers its bloggers does not pull images from posts. Images help a viewer gain more information instantly, even before having to read.
If you want an image to show up for each post in the Recent Posts widgets, you can do it using a third-party service.
Add images in a “Recent Posts” widget using Widgetbox
Visit Widgetbox, sign up and go to the Make a Widget page
Please choose Blog Feed, choose Basic and enter your Blog or Feed address.
Make the necessary customization, save widget and agree to their “Terms and conditions” and then again click “Save widget”.
Click the “Get widget” button and choose Flash (not javascript) and modify it so that it works in your wordpress.com blog. Please read the following post to learn how:
How to have Flash embeds in a wordpress.com blog
Paste the modified code in the sidebar using a text widget and you will have a “Recent posts” widget that also pulls an image from the latest posts! 
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Is there a way to make it go to the next line after the title?..