Well, on the first pic you'll have to use the stamp tool. It allows you to select a part of the background and "stamp" over the vehicle. Bear in mind that since I don't have that much experience, this is probably a harder way.
On the second pic, since you have to extract the figure, I'd recommend selecting the magic wand tool to get the top part surrounding the guardsman, and the spaces between his chest and his body.
You can do it all in one go, just select the larger area with the wand (it will select most of the white around the guardsman) and then hold shift. The wand will now have a little + next to it.
Now you pick the spaces between the arms. If you accidentally select more than you'd want, try a higher tolerance (that is, a lower number) or to subtract hold down alt (if I remember the shortcuts).
Not sure if this is what you want, I'll get both pics and launch
PS to try it out
EDIT: I don't know if this is what you wanted. I had to make extensive use of the stamp tool. Once everything was selected around the trooper, I used
ctrl + shift + i to invert the selection and
ctrl + c to copy it. Afterwards, it was paste as a different layer over the previous image (just
ctrl + v). This way I could use the burn tool to go over the sides, that were left with a white halo because the trooper had a lighter background.
The letters on top were slightly corrected using the stamp (especially the S in Service, as I was a bit careless when erasing the tank).
But I would recommend trying a different approach to these posters, like getting high-res pictures (these ones were full of artifacts, which makes it harder to work with and dulls the final job) or outright copy.
I must get my hands on some more, this is kinda cool
I hope I didn't forget anything. Sorry 'bout the lousy
ps, too, but I'm using a laptop (and 11.1" at that) and the brightness might be off...