How to do seamless stitching?

OpenGL OpenGL: Basic Coding
1

[ATTACH=CONFIG]1501[/ATTACH]
The right four images are transformed to the left one, I do this in the shaders.
The vertices are like this:
[ATTACH=CONFIG]1502[/ATTACH]

As you can see in the left image, there are seams in the red circles, so how to remove them in shaders.

gl version: gl es 3.0
raw image data format: rgb565

2

I want to apply alpha-blending, the progress will be like this .

But I will use this blend formula: