Simon Joinson has the following conclusion on the JPG photo output quality from both cameras:
Not surprisingly given the family ties (and the fact it's the same lens), the output is very, very similar, with color, contrast and saturation almost identical. Look a bit closer and you can see – even in a JPEG – that there are some differences. The most obvious is the EP-1's visibly better pixel-level sharpness (thanks to a lighter anti-alias / low pass filter), though we also noticed that the highlight roll-off is a little harsher than the E-620 (something confirmed in our dynamic range testing) – it's better at ISO 200, but still not as good as the E-620. Overall though, it's great to see that Olympus hasn't just delivered on its promise to match SLR quality – it's actually surpassed it.
The lens used on both cameras was the Olympus 50mm f/2.0 Telephoto Macro ED.