A significant downside to the <picture> element, and alternative image formats in general, is that when most users wanna download the image they expect an image format they already know how to work with. To most users an .avif or .webp are an annoyance because they reasonable expect most of their tools to be unable to open these.
It's disappointing that browser vendors haven't picked up on this and offered a "Save as PNG/JPEG/GIF" option when downloading images, but for now if it seems reasonable that if any user would want to download an image you're displaying then you should probably stick to the legacy formats.
Google search result do this weird trick. When you hover on a link the line at the bottom the your browser window shows the actual URL. But if you do "copy link URL" on it, you get a Google tracker URL in your clipboard.
Couldn't one do the same thing to make users get jpegs when they try to save a wepb? How bad would it be?
It could be used but this really seems like websites trying to "fix" browser UX. In cases like this where the problem is generic it seems like it is best for the browser to provide the UX it thinks is best for the users (possibly with preferences to allow the user to decide globally without needing to configure every single site).
A significant downside to the <picture> element, and alternative image formats in general, is that when most users wanna download the image they expect an image format they already know how to work with. To most users an .avif or .webp are an annoyance because they reasonable expect most of their tools to be unable to open these
Certainly not the case with WebP, which was announced by Google 12 years ago. On a recent version of macOS, Preview, the Mac’s default image and pdf viewer can open WebP and AVIF files, making it easy for Mac users to convert to another format if they wish. Also 3rd party graphics apps have supported WebP for years now.
AVIF support isn’t as widespread yet but that will quickly change now.
BTW, the iOS defaults to saving photographs in HEIC, which the average consumer has never heard of.
It's disappointing that browser vendors haven't picked up on this and offered a "Save as PNG/JPEG/GIF" option when downloading images, but for now if it seems reasonable that if any user would want to download an image you're displaying then you should probably stick to the legacy formats.