When images are sliced vertically, thin white lines are visible between the image slices in the Gmail app on Android.
This has two possible causes.
If the white lines are also visible in other clients, review the code and image slices to verify that no image widths exceed the container size.
If the issue is isolated to Gmail, add inline-style “display: block; width: 100%” to the images.
<img src="image.jpg" alt=" " width="640" border="0" style="display:block;width:100%" >