yup, agree with ckiang and clive. Don't need DSLR to tell you your focal length. You can just read it off the lens! And yes, you can make a rough gauge judging by the photo roughly what focal length was used, and even what shutter speed and aperture in more obvious situations (e.g mist-like water flows won't be taken with a fast shutter speed, likewise, blurred backgrounds wouldn't be taken with a small aperture.)
It is easy for a DSLR. But what about a normal digicam? Normally we just use the zoom lever switch to zoom in or out the lens. Other than the max tele and wide zoom we can't really tell what focal length we are in when shooting in between right?
I am just curious that they were able to come out something like "76mm" for focal length when the photo was taken..
Almost all the digicam (DSLR or non-DSLR) nowadays support EXIF which will write additional info such as shutter speed, aperature , focal length, iso speed etc to the picture when it is taken. No need DSLR to do that.