I'm using an analog camera, Olympus OM-1. Lately I've been developing my roll, and found some weird dark area along the surface of the film. This dark-area-thingy only appear during outdoor and sunny photos, but during or indoor photo, they don't appear anymore. Can anyone help?
Seems like your shutter curtain is damaged or needs a CLA (Clean-Lubricate-Adjust)
At faster shutter speeds part of the image gets blocked by the shutter curtain. The slower shutter speeds seem fine, which is illustrated by your indoor shots not having any dark areas.
Getting shutters repaired is an expensive task and oftentimes it is a better option to buy a new body.
Your camera has mechanical first and second curtains. At fast speeds, first the first curtain starts to move, and a bit later the second curtain starts to move, WHILE the first curtain has not completed its movement. So, there's a small slit scanning through the film.
Your shutter curtains appear to move from left to right (or vice versa), not from top to bottom (or vice versa), based on the defective picture.
I assume one of the shutter curtains is not moving exactly at the speed of the other of the shutter curtains. Thus, the slit is narrow or nonexistent at part of the scan range, whereas it's correct at other parts of the scan range.
As timvrhn explained, a clean-lubricate-adjust operation could help, but you never know if it does. Given the low prices of film equipment, you should be able to find a working replacement camera, although Olympus OM-1 is not exactly the cheapest camera to be purchased second-hand. Based on my market search (of only one data point, though), a working OM-1 probably costs twice what a CLA operation costs.