With the 'Quick Selection Tool' map out the background (the area you don't want) and delete it. This should fill it white. Then use the 'Magic Wand Tool' to completely rid of it.
Drag your background image into Photoshop. I just used one from Google Images, and you may have to save the image to your computer before you can insert it into Photoshop.
Insert the image behind you LEGO image and resize it so it’s in proportion.
Now use the rubber tool with a hardness of 0% to go around the edge of the LEGO image to it blend in a bit more. Don’t worry about this too much though.
For Windows users, Press Ctrl+U to bring up the ‘Hue/Saturation’ window. Use the bottom two sliders to adjust the colours of the images so they’re similar. This step isn’t too important, as you can see from the next image that there’s no massive difference.
Create a new layer (Ctrl+Shift+N) and fill it with black. This is where we begin to create the snow.
Go up the Filter > Noise > Add Noise and this box will come up. Ensure it’s set to ‘Gaussian’ and ‘Monochrome’ and choose an amount that seems suitable for you image; for close ups like this, I recommend a high amount. Press OK.
At the side, set this layer to ‘Screen’. This will get rid of the black in that layer and you can now start to see the snow.
Now go to Filter > Pixelate > Crystallize. Set the Cell Size to around 10. Press OK.
Go to Filter > Blur > Motion Blur. I suggest using numbers similar to what I’ve used, but experiment as it can be slightly different with every picture you use.
Now set the opacity to around 50%. However, the higher the opacity the thicker snow you’ll get. Again, experiment with this.
For this stage I saved the image as a jpg. and inserted it in a free software called PhotoScape. I went to Filter > Film Effect > Velvia High. There’s a list of effects to choose from so choose one that fits your image.