Board Thread:Support Requests - Getting Technical/@comment-896291-20140625091619/@comment-452-20140625212537

Which wiki is this happening on? I'd like to check the problem.

And yes, when the mime-type does not match the extension, there are 2 solutions:
 * Simply rename to the correct extension
 * Open the file and save it - this rewrites the file as an actual PNG instead of a renamed JPG.

However, converting media files is generally frowned upon due to the loss of quality, especially if you're up-converting like this. PNG is a lossless format, and so has a larger filesize. JPG is a compressed format, and has a smaller filesize. Converting a PNG to a JPG to reduce the filesize is okay, and normally unnoticable in photos. Converting a JPG to a PNG will increase the filesize, but will be pixel-identical to the smaller JPG, and may mislead people as to the origin and quality of the image. (If I'm looking for a high quality image, I'll search specifically for PNGs)

Lady Lostris wrote: The only instance I can think of when said message appears is when someone tries to upload a new file over another and the extension doesn't match.
 * 1) Create or acquire a genuine .jpg file.
 * 2) Rename that genuine .jpg file to .png
 * 3) Attempt to upload to any mediawiki site
 * 4) Observe the error message