From what I can see:
It appears to have been taken with a cell phone or tablet, which will be very challenging to use for stock photography (although it is usually possible to use a phone/tablet, if you work within the devices limits).
Aside from the technical flaws, you would also need to submit a model release for each of the people sitting on the bench.
In addition to the issues noted by madscica I think the white balance is too blue.
Thank you! The photo was actually shot with a Leica camera. I see your points, it probably doesn't fit as an item for stock photography. Just one thing: none of the people on the bench is recognizable, do I still need a model release in this case?
I think you understand "not recognisable" differently from us. It doesn't mean "recognisable famous person" for example. It means "this person (or someone else) could identify who was in the picture". There are many ways they might identify themselves; face, hair, distinctive clothing, the combination of clothing of the full group, combined with the day and the setting. The person on the right is sure to recognise himself, and may well remember the day, the company, and the speedboat.
Yes, you will need a model release as the people, especially the guy to the right are recognizable.
These are important questions to ask before you submit.
Meanwhile, read these links: