Line problem

[ningen58]

Whenever i stitch something there is always that line, is there any fix for it or am i stitching it wrong?
Example: https://imgur.com/a/YN9cHIg

[spillerrec]

First of all:

1. You are using a very old version of Overmix, try out the newest 'pre-release' on the releases page. I probably shouldn't have marked them as pre-releases in the first place.
2. Overmix was really intended to be used with lots of input images (50+), to help reduce compression artifacts (the pre-release supports reading video files directly) and it helps greatly if they are in order. It should still work with just 2 or 3 images, but it might not give much value over Photoshop which I believe has an auto-align feature.

The first stitch you show, the brightness change during the scene, so the first and last frame does not match up in regards to brightness. Overmix does not attempt to fix this. (#127 might improve it slightly.) This is usually not an issue if you use all available frames as the transition gets smoothed out. (However the mouth movement gets smoothed out as well.)
You can see an example of that here: https://imgur.com/a/gIv7hQw

For the second stitch, it was not aligned properly and you can see two unrelated areas overlap. It might be because of the small overlap between the two images, but it aligned just fine with the newest version. It does however contain parallax, with Senku's hand and background moving at a different speeds. I haven't seen any software being able to handle this correctly, if you look in your Photoshop stitch you can also some lines being broken because of this. If you stitch it with Overmix using all the frames, the moving parts end up blurry instead. (The first stitch actually also contains a slight parallax effect in the background.)