Image Processing: Morphological Processing, Segmentation, Object Identification and Localization.
Should be good in linear algebra, matrix, if worked on OCR system will be a plus.
Feature Engineering: Feature Extraction, Feature Selection, Sample Estimation, Principal Component Analysis, Linear Discriminant Analysis, etc.
Classification: SVM, ANN, Bayes, Decision Tree, Random Forest, etc.
Clustering: K-Means, Hierarchical Clustering, Density-based spatial clustering of applications with noise (DBSCAN), etc.
Model Selection: Precision/Recall/F1 Score, K-Fold Cross Validation, Overfitting, Underfitting, etc.
Natural Language Processing:
Named Entity Recognition, Information Retrieval, Document Classification, Query Parsers, Language Modelling, Grammar Generation.
Advance Machine Learning: Convolution Neural Networks, Recurrent Neural Network, Long-Short Term Memory, Application of these techniques with respect to computer vision and natural language processing would be a plus.
Technical Skills: Python, python libraries: numpy, pandas, sklearn, tensorflow, NLTK, etc.textblob, genism, corenlp.
Knowledge of the OCR/ICR system would be recommended