Citation - Collection of images for machine learning
Let's look at what some popular image databases say:


The website for the CIFAR image databases, which are widely used in machine learning, ask that you cite them.


  This tech report (Chapter 3) describes the dataset and the methodology followed when collecting it in much greater detail. Please cite it if you intend to use this dataset. 
  
  Learning Multiple Layers of Features from Tiny Images, Alex Krizhevsky, 2009.

Another often used database, the MNIST handwritten digit database, does not contain citation information, but a search on Google Scholar shows over 450 papers citing them.


It sounds like these features are an important point of your work and are extracted from training on the images. You should definitely cite the database for in your work. You should also cite them in the future if you are just using these databases to evaluate a technique (like object or hand writing recognition).

There's little harm to be liberal with citations.