Heatmap of lesion frequency

I have hundreds of x-ray images of the same dimensions where I manually mark the lesions of interest.
I was wondering how I go about combining all these “markings” to overlap, and to create a heatmap of which areas on the x-ray specifically have higher frequencies of these lesions occurring (red more frequent to say, blue/black, less frequent).

One suggestion would be to convert all your markings into binary images (lesions of interest white, everything else black), create a stack of all the binary images and do an average intensity projection for the stack. The average intensity will be brighter than the low frequency areas. You can then apply any LUT you like to colour code the frequencies. Obviously, this will only work if your images don’t only have the same dimensions, but are also aligned so that the same structures are always in the same place. If that is not the case, you will have to do some form of mapping/registration to a common coordinate system.
Hope this helps,