Check Geometrical Match of Two Scanned Images with Standard Linux Tools

I have two images (taken with a scanner at the same resolution) and I want to superimpose them on the screen to see how well two features match to each other after applying the right shift and rotation to one of them (like a combination of a front and the back side of a printed circuit board). The two images are shifted and rotated with respect to each other with unknown parameters (dX, dY and rotation angle phi). In my case there are no straight outlines to calculate a matching corner or measure the relative rotation angle between the two scans. In Gimp there are tools to flip images, to shift an image and to rotate them. One can superimpose one onto the other by using different layers and applying some degree of transparency to the uppermost layer. Using Gimp's **Tools>Move** and **Tools>Rotate** one after the other is very cumbersome. There also is an uniform transformation tool in Gimp, but this one also interactively changes the size and applies other geometrical transformations, not only translation and rotation. I see nothing in them to pin the additional parameters. I want to align the two images by visual inspection, shifting and rotating one of them (e.g. in 50% transparent mode) to the other one for a best fit. - Did I oversee the right tool in Gimp? - Or which other standard FOSS tool (and which function in it) do you recommend for this purpose?