Emperor Penguins, on the ice.
This is the photo with the background selected and deleted, after adding alpha transparency in the GIMP.
And this is the result, when saved as a .png file with the transparency still included. JPEG does not keep the transparency, so it would show with a white background.
Result of selecting background and cutting it, with alpha channel for transparency.
Here's a second attempt, using a combination of colour-select, then free-select+/- to add or subtract from the selection. Able more easily to fine-tune the selection.
Almost the same image, but optimised for the Web when saving, using .gif for the smallest file size.
Reduce in size, once again.
Gimp right-click-menus. Here Dockable Dialogs. Note that many commands have 'hot-keys' assigned to them. This is even quicker, once you know them.
Adding areas to the selection with the quick mask, painting 'white' to add and 'black' to remove, areas to the selection. Good for including areas excluded by by-colour select, etc.
Navigation window - easily find any part of image with high magnification.
Right-click menus - Dockable Dialogs, they're all here!
Navigation window - easily find where you are in an enlarged picture, or adjust back to normal zoom.