What's the easiest method to store EXIF data from photos inside a Database (MySQL during my situation). To a photograph discussing site.

Do you know the most significant Tags, and what exactly are discardable?

It's difficult for all of us to determine which is essential for you personally. One approach may be to keep all of the qualities inside a table produced something similar to this (approximate SQL syntax):

create table exif_info (
    photo_id integer,
    name varchar,
    value varchar
);

Each row within this table affiliates one EXIF property with one photo. Which means you would want a lot of rows to carry all of the EXIF qualities for any single photo, but this is just what relational databases are great at.

In by doing this, you are able to store all of the available information without needing to decide ok now what may be important later.

For the second question...

Picasa

  • Time and date the photo was taken
  • Camera make &lifier model
  • Resolution
  • Orientation
  • Focal length
  • Aperture
  • ISO speed
  • Gps navigation latitude and longitude

Flickr

  • Camera
  • Exposure
  • Aperture
  • Focal Length
  • ISO Speed
  • Exposure Prejudice
  • Expensive

Really, I would suggest storing EXIF like a blob (json?) since there's great variability across products that generate EXIF. It might be simpler to drag that like a chuck after which work on it.

If this sounds like for any photo discussing site, you most likely wish to keep IPTC info too, most likely very much the same.

See http://bret.appspot.com/entry/how-friendfeed-uses-mysql

EXIF is metadata. Why don't you make use of a data format designed in the ground-up to cope with metadata? EXIF might be easily put in RDF, that has a lot of tools, libraries and storage options.