How to steganographically embed data in cropped/resized images?
This is a big research field with a lot of different techniques. The right term here is "watermarking". Similar to steganography but with different requisites: we hide only a mark and we want to be resistant to cropping, resizing and others (blurring, compression, noise addition, ...). One approach to resist cropping is to copy the mark several times in different positions of the image. One approach to resizing is to hide information by modulating the DCT coefficients.