As of now there is no Official Method to Override the Lightbox, and it is enabled on all of the Blogger Blogs. If you don’t like the Light Box, and want to remove it from your Blog, then read on:
Blogger has now added an option to disable the Light Box. The feature is enabled by default. You can turn it Off from Settings > Posts and Comments. You just have to set “Open images in Lightbox” option to “No”
Now Click on the “Save Settings” Button
Update: Blogger has Rolled back the Light Box Feature. So there is no point in reading further.
Go to Template > Edit HTML and paste the following Code Snippet above </body>
In this Code, Blog1 is the id of your Blog Posts Widget.
Save The Template, and LightBox wont be bothering you anymore :) I use the same technique here on my Blog :)