Calling a function

Hi. I'm trying to call the function 'store_description(image)' at line
9. However when I do, I get the error "undefined method
'store_description' for Photo:Class". What can I do?

1: class Photo < ActiveRecord::Base
2: def store_description (image)
3: self.description = "size:
"+number_to_human_size(image.filesize)
4: end
5: file_column :image, :magick => {
6: :versions => {
7: "thumb" => {
8: :transformation => Proc.new { |image|
9: store_description(image) # what do I put
here???
10: image.change_geometry!('160x120') { |cols,
rows, img|
11: img.thumbnail!(cols, rows)
12: }
13: },
14: :attributes => { :quality => 50 }
15: }
16: }
17: }
18: end

Thanks!

On line 2, try: def self.store_description (image)

Okay, I've tried that, and the function runs now (progress!) however I
now get the following error:
    undefined method `number_to_human_size' for Photo:Class

If I eliminate the 'number_to_human_size' then I get the error:
    undefined method `description=' for Photo:Class

Any ideas?

Let's try this:

Change line 2 to: def store_description (image)
Change line 9 to: self.store_description(image)

If that doesn't work, try having them both be self.

Okay, I tried those both.
The first suggestion triggers this familiar error:
    undefined method 'store_description' for Photo:Class

And the second, this one:
    undefined method `description=' for Photo:Class

Surely what I'm trying to do isn't that odd?