To geo-tag a photo, what attributes are required? More than lat/lon? - iphone

Question

I am trying to geo-tag photos taken with the iPhone camera. Since I'm not saving the photos to the camera roll, the photos do not have any EXIF data.
So, what elements are required in valid EXIF data? I think I have written the latitude, longitude, and altitude to the EXIF data, but when I export the photo, there doesn't seem to be any EXIF data.
I suspect that for a service like Flickr to display the EXIF data, I need to add more than just the latitude and longitude or some such foolishness.
Anyone have any experience with writing EXIF data?
EDIT #3: Aha, got it now! Thanks for your help. What I had to do to address EDIT #2 was add the make, model, and software.
EDIT #2: Thanks to the first respondent (who I will give the correct answer two regardless), my photo is now being geo-tagged, but now I have a related question.
The photo gets automatically located when I upload it to Flickr (when I go to map it it suggests the location), but it doesn't show the nice chart of EXIF data.
This photo is geo-tagged. but no nice chart of EXIF data on this page:http://www.flickr.com/photos/33766454#N02/3980488205/.
This one exported from the camera roll shows a More Properties link to show the EXIF data in full: http://www.flickr.com/photos/33766454#N02/3978868900/
Now I'm wondering what I have to do get Flickr (and also Picasa on my desktop) to display the link to see the EXIF data. When I look at the photos properties on my Mac too, I don't see any EXIF data, but I know it's there.
EDIT: Based on the advice in the first two answers, I set the suggested EXIF tags and inspected them in EXIFTool. Unfortunately, though the EXIF data shows up in EXIFTool, it doesn't show up when I upload to Picasa or Flickr. Here is the output from EXIFTool. Any idea what I still might be missing?
~/Downloads: exiftool My_Photo_-_10-4-09_5_22_20AM.jpg
ExifTool Version Number : 7.96
File Name : My_Photo_-_10-4-09_5_22_20AM.jpg
Directory : .
File Size : 287 kB
File Modification Date/Time : 2009:10:04 05:22:51-07:00
File Type : JPEG
MIME Type : image/jpeg
JFIF Version : 1.01
Resolution Unit : None
X Resolution : 1
Y Resolution : 1
Exif Byte Order : Big-endian (Motorola, MM)
Orientation : Horizontal (normal)
Color Space : sRGB
Exif Image Width : 319
Exif Image Height : 480
GPS Version ID : 2.2.0.0
GPS Latitude Ref : North
GPS Longitude Ref : West
GPS Altitude Ref : Above Sea Level
Image Width : 319
Image Height : 480
Encoding Process : Baseline DCT, Huffman coding
Bits Per Sample : 8
Color Components : 3
Y Cb Cr Sub Sampling : YCbCr4:4:4 (1 1)
GPS Altitude : 0 m Above Sea Level
GPS Latitude : 37 deg 19' 54.08" N
GPS Longitude : 122 deg 1' 50.63" W
GPS Position : 37 deg 19' 54.08" N, 122 deg 1' 50.63" W
Image Size : 319x480

Answer 1

I've done this to geo-tag photos which Picasa will recognise, for Picasa you need to add the following tags:
GPSVersionID ("0 0 2 2 "), GPSlongituderef ("W" or "E"), GPSlatituderef ("N" or "S") and also GPSAltitudeRef ("Above Sea Level")
Values in brackets are the ones I used. These are in addition to the lat, long and altitude tags. As Brian mentions exiftool is excellent for examining and modifying EXIF tags.
EDIT
Output from exiftool:
ExifTool Version Number : 7.01
File Name : bleatarn.jpg
Directory : .
File Size : 3 MB
File Modification Date/Time : 2008:03:01 12:43:44
File Type : JPEG
MIME Type : image/jpeg
JFIF Version : 1.1
Resolution Unit : None
X Resolution : 1
Y Resolution : 1
Exif Byte Order : Little-endian (Intel)
Software : Picasa 3.0
Exif Version : 0210
Interoperability Index : Unknown ( )
Interoperability Version : 0100
Image Unique ID : 6fda6fa9628b8615d99abc81663c9b01
GPS Version ID : 0.0.2.2
GPS Latitude Ref : North
GPS Longitude Ref : West
GPS Altitude Ref : Above Sea Level
GPS Altitude : 0 m
Caption-Abstract : Blea Tarn
Image Width : 3151
Image Height : 1375
Encoding Process : Baseline DCT, Huffman coding
Bits Per Sample : 8
Color Components : 3
Y Cb Cr Sub Sampling : YCbCr4:2:0 (2 2)
GPS Latitude : 54 deg 25' 44.33" N
GPS Longitude : 3 deg 5' 27.44" W
GPS Position : 54 deg 25' 44.33" N, 3 deg 5' 27.44" W
Image Size : 3151x1375
Only difference I can see is that GPS Version ID is different, and you're Big-endian rather than little-endian (that shouldn't matter, should it?)

Answer 2

This may help. It details how to copy the geotagging data to a photo without geotagged data, and details the EXIF fields used by exiftool.

Answer 3

I would also set GPSMapDatum, as the EXIF standard strongly recommends including this tag. The value would be "WGS-84", assuming your coordinates come from a GPS unit or are based on common web maps or any other current source of location data. (If you're using a different datum, it'd be better to convert it to WGS-84 anyway, since I suspect most viewers just assume that to be the datum.)
If you're not familar, a map datum tells how to interpret the latitude and longitude values. Since the earth is not a perfect sphere, there are many ways the coordinates can be interpreted. Using the wrong interpretation can sometimes have a significant effect on where the marker will end up on a map.