How to adjust watermark size regarding the size of the picture ?

Hello,

I'm a beginner with photoshop.
I'm taking photos for a dance association and I would like to add the logo of the association in the corner of the photos for all the photos (around 50/week). I found a way of doing it (may be not the best, but it works) : I wrote a small serie of actions (import the logo / align down / align left / flatten image / save / close). Then I use Batch processing to apply this serie of action on my photos.
The problem is that I crop most of my photos so they don't have the same final size. But I could not find a way to adjust the size of the logo to match th size of the photo : sometimes, it is too small and sometimes too big compared to the size of the photo.
Do you have any idea how I could solve my problem (without manually setting up the size of the logo each time).

I tried to look on internet but could not find any help regarding this problem.

I hope my problem is clear enough. If you have any question, let me know.

Thank you in advance for your help.

Stéphane