It means that we cannot determine the mime type using any means known to PHP, but it also might just be if you are using an older version of the plugin? There were some issues previously with the finfo plugins on PHP pre-5.3, but they should be resolved now (should, but perhaps we’re missing something).
Your PHP version might also be useful.
I’ve also been getting this error – with images with large dimensions. When I reduced the pngout optimization level I stopped getting errors with large images.
I think its caused by some kind of PHP timeout – PHP gives up waiting for pngout to finish
I’m currently experimenting with increasing PHP timeouts – I’ll let you know how I get on – in the meantime, try reducing your compression settings, and try uploading some images with small dimensions to see if your symptoms are the same as mine…
Andre, I think I might have overlooked the obvious issue as Jon pointed out. It is probably because pngout or optipng is taking too long, and so the image metadata never gets sent back to the database. The solution is to decrease the optimization levels, and potentially stick to just optipng OR pngout (not both).
Jon, just to clear up some confusion around the PHP timeouts, it is likely you will not have any success in increasing those. I played around with that stuff when I was first developing this plugin, and I discovered that the exec() function is essentially exempt from the PHP limits, because it isn’t running any PHP code while it waits for the optimizers. The PHP limits ONLY apply to time spent processing actual PHP code, not time spent waiting for commands run by exec(). That said, many webhosts will kill long-running processes, so there is probably some other limit there. On my webhost, I have issues with this, but on my local dev-box with a very low PHP timeout, I can let a bulk optimize run for over 2 hours with no issues.
