Google added the feature to always show images in the emails a month ago on the desktop version, and now on Gmail Android you can select to display images automatically.
To disable / enable the Always Show Images on Gmail Android, do as follows:
1. Open Gamil application on your Android phone (Make sure you have the updated version, Update Gmail)
2. Go to Settings and select the account you want to change options
3. Scroll down, and under Data Usage settings, tap "Images"
4. Select "Always Show", so the images will be automatically loaded, and select "Ask before Showing", which is an Undo function for the previous one, and always asks you before loading images