But this is limited to putting the signature in the same position in the photo.

Let's just say the general situation, open the image, and then press F7 to open the layers panel.

Then drag the signature map into PS, and you will see a new layer in PS, whose size and position can be adjusted at the same time.

Adjust the size and position.

Select the signed layer and choose the blending method according to the color of the photo. The default is normal. You can use positive film to stack the bottom and filter the color. You can try them one by one ... mainly these two.

Then save it in jgp format.