Canon ELPH 520 HS has a
10.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features DIGIC 5 processor. On the other hand, Olympus E-PL5 has a
16.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor .
Olympus E-PL5's sensor provides 6MP more than Canon ELPH 520 HS's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the ELPH 520 HS and E-PL5 sensor size comparison.
As seen above, Olympus E-PL5 has a 8.0x Larger sensor area than Canon ELPH 520 HS. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.