>>>About 99% of it is jpg, so a jpg-only solution would work perfectly. The remainder can be converted to jpg :).
>>
>>IIRC, JFIF is the hardest header format to read :-{
>>Link to a C version you might be able to convert : http://www.64lines.com/jpeg-width-height
>>No idea how reliable it may be tho.
>
>The faithful old AcdSee manages this quite well and rather fast, and it's the same old version from 1998. So the format hasn't changed.
>
>>Occurs to me that if the list of images changes only rarely you could use LoadPicture() when a file is added and store filename,width and height in a lookup table for future use?
>
>That's what I did first, but then that was an early version of this, back in the times when there was never enough disk space. Now I'm reconsidering... though the above link gives some hint to the nature of the JPEG header(s). I was also storing a minimal webpage which would display the picture in a browser object, plus some data (mostly date and time, nothing much). Well, an interesting pastime for, I guess, november, when the weather is... well, you'd call it nice.

You'll find plenty of info here http://www.fileformat.info/index.htm
eg PNG: http://www.fileformat.info/format/png/corion.htm

Enjoy