How many levels of research are there for each enemy in Bioshock?

Is it possible to know how many levels of research there are and what level I'm at? I see big letters (A, B, C) in red, but I understood that it was the quality of the picture (centered, enemy action, distance).

For example, with the "Spider Splicers", I finished the first level of research (I've filled the progress bar once). However, if I take a picture again, the progress bar restarts! So I guess there are several levels of research?

How do you know how many levels there are and at what level I am?

There are five levels of research for each 'creature' in the game. I'm not sure if there's a way to know what level you're currently at. Once you've completed all of the levels for a specific creature type, your camera won't accept photos of those creatures anymore.

A bit more about researching, from the Bioshock Wiki:

The Research Camera does no damage itself, but it is a deadly addition to the arsenal. It is equipped the same way as a weapon, and uses film to take pictures that unlock biological weaknesses and hidden secrets through research of every Splicer, security device, and Big Daddy.

In each tree, there are five levels of research that require increasingly more photos to complete. On the first, third, and fifth levels of completed research, a permanent damage boost is applied against the researched enemy type. The second and fourth levels of completed research yield various Gene Tonics and other bonuses that are extremely useful. Little Sisters are the exception, as a permanent increase to health and EVE is given for each completed level of research.

The Damage Research tonic increases effectiveness of damage bonuses from research. The Research Camera cannot be upgraded.