Image registration algorithms for images with varying distances
Since you need to implement image registration for real-time your should have fast registration algorithm, such as differential total variation (DTV) or binary gradient angle descriptor. However, these methods implement for challenge dataset or multimodal in consideration of your images are mono-modal meanwhile these methods should work perfectly in your case.

Your algorithm should include these steps:


Image descriptor to extract the images features.
Feature selection: find the most similar features (this step is important to remove outliers which is common)
Minimise the distance between the related image features to get the optimal transformation.
Apply image transformation on the floating image.