It seems that you are going to overfit this dataset.
Have you tried to use image augmentation, collect more real images or generating synthetic one? 500 images with a from scratch model it seems to me a little bit too small dataset specially if you want to perform “in the wild”.
For the TF.js converter the Readme was moved here:
  
      

      github.com
  

  
    tfjs/tfjs-converter at master · tensorflow/tfjs 1

  master/tfjs-converter

  A WebGL accelerated JavaScript library for training and deploying ML models.