While it is technically possible to upload a PNG image as show main image (meaning there is no error message saying "Please do not use PNG as it is not supported, use JPEG instead"), the site editors seemingly just can't see the uploaded picture in their browsers, so they reject it. One editor also apologized to me for "not seeing the image" as explained that it is possible because of the PNG format. Can you fix this? Either by making the user aware of the fact that he just uploaded an invalid graphic format, or, even better, by simply supporting PNG (as it is widely common)? Thank you.