Open your picture in Gimp. Crop it getting rid of extra image you don't want.
Now remove the background. Use what works best for you. Sometimes I use the eraser while other times I use one of the selection tools.
Now you have the option of selecting the flower then copying and pasting it onto a transparent background thus removing the white background as in the example below.
With it pasted onto a transparent background, I sometimes take the opportunity to adjust the black and white levels a bit more.
For speed's sake, I simply wanted to show you what the black and white drawing can look like.
It takes me a good part of the day to complete one black and white line art.
Examples of ways to use your line art are below:
Retro sunflower picture Flower Store business cards
Schipperke dog ball cap (hat)
Schipperke Picture Mesh Hats by Visages
Make your own personalized hats online at Zazzle.
Schipperke picture clock
Cute Ferret Picture T-shirts by Visages
Design unique custom printed t shirt at zazzle.com
Ferret picture playing cards
Cute Ferret Picture Card Decks by Visages
Browse more Playing Card Decks online at zazzle.com