In a small bowl, sprinkle gelatin over 1/2 cup milk. Let stand 1 minute, then stir and let stand about 10 more minutes for gelatin to soften.
In a medium saucepan, whisk remaining 1 1/2 cups milk and 1/2 cup sugar over medium-high heat until steaming, about 3 minutes. Add gelatin mixture and whisk gently until it dissolves, 2 to 3 minutes. Let cool 15 minutes.
In a large bowl, whisk yogurt with vanilla and almond extract until smooth. Pour and stir milk mixture through a fine strainer into yogurt, then whisk mixtures together.
Oil 8 ramekins (2/3 cup size). Divide yogurt mixture among ramekins. Chill, covered, until set, 4 1/2 hours and up to 2 days.
Ten minutes before serving, rinse and drain blueberries. In a bowl, stir berries with 1 tbsp. sugar and cardamom. Stir occasionally until sugar dissolves.
Run a small metal spatula between panna cottas and sides of ramekins to loosen. Immerse ramekins 1 at a time to just below rim in hot water until edges of dessert soften, 20 to 30 seconds; lift out and dry bottom of ramekin. Invert a small plate over each. Hold plate and ramekin together and give a firm shake to release panna cotta, easing it out gently with the spatula if needed. Spoon blueberries over panna cottas before serving.