Jan.ai might be a good starting point or ollama? There’s https://tales.fromprod.com/2024/111/using-your-own-hardware-for-llms.html which has some guidance for using jan.ai for both server and client

You’re looking for something to export the image at a lower resolution (resize) rather than something to compress the image. Any open source gallery/image editing app should be able to do this.

One example would be “image toolbox” on FDroid. I’ve not used it but it seems to have the feature you need