To clarify, the issue is only with the resized images (thumbnail, small, etc) created when we upload images to Wikidot since these are created as JPG images regardless of the original file format and JPG does not support transparency.

As I commented the thread referenced, Wikidot uses ImageMagick to create the thumbnail, small and medium versions of images when we upload them. I have often wondered why all images, regardless of original format, are always converted to JPG when creating these different sizes. It might be a limitation of ImageMagick, or it might have been easier to implement by using a single file format. If the latter is the case, it would make more sense to use PNG as a standard to avoid this issue (even though the files sizes are typically larger).

The workaround is to not use the "small", "medium", etc. parameters. You can either resize the image before uploading it or use specific height and width parameters to scale the image.

-Ed

No thumbnails Wikidot generates are transparent. So no matter if you use them in tabview or anywhere else. JPEG format is used widely (not only at Wikidot) as lossy compression for images, which gives good compression ratio, which makes it ideal choice for thumbnails. JPEG does not support any kind of transparency so unless we change format we store thumbnails in, this won't be changed. And honestly I don't see a reason to switch from JPEG.