It's actually a sharpened version of the original image, which is 35kb.

https://en.wikipedia.org/wiki/File:Rongorongo_B-v_Aruku-Kure...

Wikipedia only accepts freely-licensed [0] images where there is a possibility of obtaining them. [1] If you manage to get a better photograph, you are welcome to replace the image. If you know of someone who has such an image or could take one, you can request them to license it appropriately.

[0] Think things like Creative Commons or public domain. The license has to allow derivatives and commercial use for anyone, not just Wikipedia.

[1] So exceptions would be for dead people or things that we are very unlikely to get new pictures of. Doesn't apply when you could try getting a license or if there is an existing free image.