How to splice irregularly spaced sprite animation sheets

How to splice irregularly spaced sprite animation sheets

I would like to incorporate some of the animated sprites that I've found on this site into a game that I'm building. In the past, I've used animated sprites built either from multiple frames stored as single images, or from sprite sheets in which the frames are regularly spaced across the sheet (e.g. each frame is a 32x32-pixel square). Many of the sprite sheets here, however, have their frames spaced irregularly on the sheet: the frames seem to have been squashed together as closely as possible in order to produce the smallest possible sprite sheet. E.g.:

In order to chop that sprite sheet up into a number of animations, I need to know the dimensions of each frame. Presumably the artist had specific dimensions in mind for each frame when creating the animations -- so has that information just been lost? I would have expected either the dimensions of each frame to be marked in a different colour (with the borders being discarded after splicing), or for some frame information to be provided along with the sprite sheet, e.g. a text file saying that for animation 1, frame 1 begins at position x,y and has a width of w pixels and a height of h pixels, and so on.

Of course, I could open up the sprite sheet in a bitmap editor, then splice it manually by guesswork, using a fixed point of reference (such as the eye in the above example), but, especially when the animation is associated with locomotion through a scene, that point of reference might be intended to move within the frame during the animation (i.e. the blob's eye moving up and down, and side to side, as the blob squishes itself about to propel itself forward).

Am I missing some hidden information contained in the sprite sheet, or are we expected to work out the splicing points manually in order to make use of sprite sheets like this?

I'm sorry if this has been asked before elsewhere (I couldn't find anything in the FAQ or through searches), or if I've asked the question in the wrong forum (it's kind of on the boundary between art and programming).