Card counting online is extremely difficult, thanks to the use of RNGs which randomly reshuffle the deck after each turn. You'll be far more successful playing at a land casino with a real-life dealer and physical deck of cards.
Counting cards at electronic blackjack machines is generally not possible for a few reasons. Here is why: Continuous Shuffling: Most electronic blackjack machines use a continuous shuffling mechanism, which means that the cards are shuffled after every hand, resetting the count each time.
