The movie's scientists took dinosaur blood from the stomachs of ancient mosquitoes which were caught in prehistoric tree sap. This sap crystallized and trapped the insects, keeping the blood preserved until scientists extracted it. The computers then analyzed the segments of DNA and filled in any missing spots with the DNA from frogs.
As real as the movies make it seem, this is not yet possible and may never be. There are several reasons for this. First, the DNA chain is much too long to fill in all the blanks. There are billions of instructions contained in the DNA chain. Second, the DNA only keeps for about 50,000 years. Over time it disintegrates, making it harder to read. At more than 100 million years old, it is almost impossible to reconstruct these chains.