Is there usury in the mentioned transactions—which include purchasing a "CashU" card charged with $10 for 2,0 Algerian Dinars, with an immediate exchange between the two currencies—and is it permissible to obtain a "MasterCard" in this manner?

The transaction is permissible if the amount is deposited in Algerian currency into the account, then dollars available on the card are purchased with that amount, and the transfer occurs between the two accounts. This is because constructive possession takes the place of actual possession in currency exchange. This is in accordance with the resolutions of the Islamic Fiqh Academy, which state that banking entry of a sum of money into a customer's account is considered a form of constructive possession that is legally and customarily valid. A delay in the banking entry is forgiven, provided the beneficiary can actually take possession within customary periods, and provided the beneficiary does not dispose of the currency during the forgiven period except after actual possession becomes possible.