LEVEL
Your photo(s) did not appear to be level.
This problem is caused by not keeping the camera completely level while making the photograph, and particularly applies to pictures of aircraft on the ground. For shots of aircraft in flight where the ground is visible (take-offs and landings in particular), the general rule is that the camera should be level with the horizon and the aircraft be at an angle.

A good method for checking if the photo is levelled is to check the vertical lines in the photo (buildings, lamp posts etc.) for being vertical. Try to avoid using verticals at the left or right edges of the photo, because these are often subject to lens distortion. In general, these problems can often be fixed by carefully rotating the picture until the verticals are truly vertical, and then cropping the picture. When using a wide-angle lens, use the verticals in the centre of the image to level the photo.

If you think you have been able to improve the photos, please re-upload them. Do not forget to include a note to the screeners, detailing what you have done to improve the image. There is a special field available for such notes. Please note that we are still very interested in having these photos in our database, we only ask that you try to improve the quality of the images as much as possible.

Image needs 0,35° CW rotation / accepted version - Photo copyright © Thierry Deutsch

no reliable references hence levelled by feeling -> rejected version / accepted version - Photo copyright © Thierry Deutsch

a good reference for such cabin shots are the headrests; keep them horizontal from left to right and you should have no level problems. Leaning CCW / levelled - Photo copyright © Tony Printezis

rejected / accepted version - Photo copyright © Walter van Bel

When levelling side-on shots, the runway is a very good reference... - Photo copyright © Thierry Deutsch

... if it's sloping however, you better take another reference (verticals of buildings in the background) - Photo copyright © Thierry Deutsch

Cockpit shots are best levelled along the outside horizon (with a wide angle lens you'll have to level point-to-point from one side of the frame to the other)... - Photo copyright © Thierry Deutsch

... or along the instrument panel - Photo copyright © Thierry Deutsch

the light pole in the background offering a perfect vertical reference (rejected / accepted version) - Photo copyright © Thierry Deutsch

Even slightly (~0.2°) unlevelled photos will be rejected, so double-check your verticals. If there are no usable verticals in your photo, a good trick is to look for a long and straight horizontal line in the background which you can take as horizon to level the shot.

And then there are these photos that just don't have any reliable level references (like the Jetstream above) or too many contradictory references. The best way to go here is to trust your feeling; level it until it feels right; you'll get the best result when looking at several well levelled pictures (you'll find a few hundred thousands in the A.net database) and then looking at yours. You'll normally instantly feel if it's levelled or leaning to one side or another.