please and thank you
You need to give examples of the old photo . Is it monochrome or colour or maybe something like a sepia print ?
Also the type of image you want to superimpose. For example adding as an integral part of the the old photo is different to say adding a watermark or caption.
Use layers then merge down:
The base layer would be the vintage photo; the layer above would be the addition.
Not sure that this what you are looking for. Please feel free to ask questions.
something like this?
It is a label:
Get the two images, the background image and the label image. The label image is a suitable size although it is possible to scale it in place a small amount
Open the background image
Open as Layers the label
Use the Move tool to position the label
If you need to scale / rotate … do it now.
Merge the layers. If you Export as a jpeg / png … then that also merges.
A 40 second animation of that https://i.imgur.com/3HYXt9W.mp4