I'll show how I went from these sources:
And created this:
First off, I created a new document and placed the 2 sources on separate layers after having extracted them from their original images. I used layer masks to select around each image and cut them out but your favorite extraction method will work just as well.
Then, I made a selection around the frog's head and copied it to another layer as well as duplicating the raspberry layer and used this duplicated raspberry for the shaping of the head. I placed the raspberry over the frog head and lowered the opacity of the raspberry, around 60% or so, so I can see the frog head behind it.
Now I use the liquify too to shape the raspberry around the head. I used varying sizes and pressures so you can experiment with what works best for the given area. I also had the "show backdrop" checkmarked so I could see the froghead underneath it. You can vary the opacities of the backdrop. Although I kept mine between 40-50%. After liquifying, I ended up with this:
Even though the shape is almost right, I need to erase parts of the raspberry to get it to better match the frog head shape. So I ended up with this:
Now that the shape is correct, I need to cut holes for the eyes and the nostril. I made the raspberry layer into a layer mask and masked out the eyes and the nostril. I also need to add some shading and lightening to get some of the features onto the raspberry like that of the frog. With some burning and dodging, alternating between hilight and midtone, and using the frog source as a guide to where the darks are, I got this:
Now that the head is finished, I moved on to the body. I made a selection of the body onto its own layer and another copy of the raspberry layer underneath it. Lowered the opacity of the raspberry layer, and I got this:
Again, with the same liquifying method, I ended up with this:
After erasing unneeded parts of the raspberry, I used layer masks on both the rasp. head and rasp. body to blend the two sections together. I ended up with this:
After this, I used the burn and dodge tools, mainly set to hilight, to darken and lighten areas of the body and make it look more rounded. The body of the frog didn't have many contours so this was enough burning and dodging that it needed:
NOTE: You can delete the frog part layers that were used as a guide to liquify each section as they are now hidden and aren't used. EXCEPT the head layer, which still has the eyes and nostril showing through
As you can see, the same processes are repeated over and over for different sections of the body until it's completed.
Next is the front arms section. After liquifying another raspberry layer on top of the arm section layer, this is the result:
After a little burning and dodging to get the details of the frog in the raspberry:
Again, I used a layer mask on the raspberry arms and blended it with the rest of the image:
Next was the back leg. Again, with a leg section copied onto another layer and another raspberry layer on top of it, I liquified the raspberry around the leg. Then dodged/burned to get the desired amount of detail:
Again, with a layer mask for the raspberry leg, I blended it into the rest of the image:
Now the raspberry frog is basically done but now I want to do something with the eyes. The original eyes had green in them and, now that the frog is all red, I want to get rid of the green and make it red.
So I created hue/saturation adjustment layer and applied it to the original frog head section layer only. To do this the adjustment layer has to be above the original frog head layer and then, by alt-clicking the horizontal line between the adjustment layer and the frog head layer in the layer palette, you create a link so-to-speak between the adj. layer and the frog head layer. Just to make sure, the adjustment layer is positioned between the raspberry head section layer above it and the frog head section below it. So I adjusted the sliders, with the colorize box checked, to get the desired red color:
Now I used a black brush on the adjustment layer to get rid of the center of the red part so there's only red around the edges of the eye like this:
After this, I decided to darken the one raspberry portion that was in the general vicinity of the "ear" of the original frog, or so I think it's the ear.
Now the frog is complete. I took all the layers and put it into a layer set so I can keep all the layers together to make it transferring over to the background image easier. It's a simple drag from the layers palette over into the background image canvas.
I wanted to use the original raspberry source image as the background. I decided to crop a little off the left and right to make it more vertical. I also cloned out the raspberry that's towards the right-bottom. Plus I cloned out the original raspberry since it's now being replaced by the raspberry frog. Don't worry about parts of the raspberry that are left since they will be covered up:
Then I dragged my raspberry frog layer set into the background image to get this:
Ok, so it looks like the froggy is floating in middair, we can't have that now, can we? I found a good source of another raspberry leaf, extracted it from the image, then placed it in the final image:
Well, almost done, except for the fact that he's not "grounded" on the leaf.
One major thing that'll make or break a good photoshop job is the use of shadows. This involved two different layers. I had one layer, set to multiply at 100% that I used a dark green, soft brush with the opacity of the brush set between 20-30% for the lighter shadows. Then, I created a layer set to normal with a soft dark green brush with varying opacities to get darker shadows. This is how it looks without the frog:
Note that I didn't get rid of everything around the leaf since it's being hidden by the frog. Same goes for the areas of raspberry that I didn't clone away from the background.
Now, with the frog back, the final image looks like this:
