I managed to solve my problem. I had mistakenly installed OpenCV by myself but since ROS Indigo already has it, some problems were ocurring. I had another error about libfreenect.so.0.6 and I solved it by writting in my terminal (or .bashrc for that matter) the following line: export LD_LIBRARY_PATH=\$LD_LIBRARY_PATH=/usr/local/lib.