Triangle in Mars Curiosity Image [Panorama Stitching Artifact]

[Hannover]

I saw in a youtube vid some claims about this image (UFO of course).
At first I thought the triangular "UFO" was due to image manipulations. Most people don't seem to realize that playing wildly with contrast and other image adjustments can create all kinds of artifacts that are not actually in the original image.

In this case it's a little different, tho.
You can actually see the triangular shape without applying any manipulation of the original image whatsoever. It's too big to a be a compression artifact. You can download the slightly compressed original NASA TIF here: http://photojournal.jpl.nasa.gov/catalog/PIA20602.

The object is visible in both the JPG and the TIF version. I suggest to download the TIF version as it is only slightly compressed.

I am curious what you guys make of it.
ETA:
Just to be clear: I am not making any UFO claims. I am simply curious if somebody with more image processing experience than me has an explanation for this artifact.

It's a big image (5000x6710 pixels) and it takes a while to spot the triangle.
To make it easier for you I created a low res version and encircled the object on the right side not far above the horizon. You can't really see it in my low res version but it is clearly visible in the high-res TIF image:

 

[Mick West]

That s not an original image, it's a stitched panorama of MAHLI images from Sol 1338
http://mars.jpl.nasa.gov/msl/multimedia/raw/?s=1338&camera=MAHLI

The image from 20:56:47 seems to be the closest
https://www.metabunk.org/data/MetaMirrorCache/e8290edaed0ff6433eedcaf562667047.jpg

Overlaid:

The triangle appears to match the corner, slightly rotated. So it appears to be a stitching artifact for merging multiple images into one image.

It's also quite possible that it's a manual editing error from cleaning up the sky. Notice there's more sky in the composite image than in the individual raw image. Also the raw images have black specks from dirt on the sensor, so the sky was probably cleaned up manually.

Note it's not intended to be passed off as a raw image, it's a composite. Only artifacts in the individual frames that make it up would have any significance.

 

[Hofnarr]

Oh swell, I guess "ufo sightings daily" will be all over this..
At first I didn't see what you meant, but with "enhancement" its visible.
As Mick said, most probably a stitching error. And it looks like its been corrected manually but this little speck was left out, I think about manually because of the hard edge at the bottom of the triangle otherwise it would fade out from top to bottom.
- Thanks Mick you were quick.

 

[Mick West]

Here I've blended three images using the program "Calico" on the Mac. Note how it has to curve the images to make them fit, which would be why the corner does not line up perfect.

Notice the uneven lighting in the sky. You don't see it so much in the ground, but in the sky it's more noticeable, and of course there's a lot of the sky missing, so it was probably manually smoothed out, with this minor editing error

 

[Hannover]

Makes sense. Thanks.