The screenshots still look extremely low-res and this could be what's causing these anomalies.
Here are a couple of things you can check:
Resolution:
Try changing the resolution ingame through the console:
Open the game again. When you're in the menu open the console with the tilde key.
If this doesn't open it it's bound to another key. In this case quit the game, delete KillingFloor.ini and start it up again. This will reset everything to default settings, including the key to open the console.
Now type "setres 'nativeXresolution'x'nativeYresolution'x'desiredcolordepth'"
In my case this would be "setres 1920x1080x32"
Confirm with enter.
Texture Detail settings:
If this doesn't improve readability either your texturedetails (including the interface texture detail, which normally can't be touched for exactly this reason!) is set too low. Open KillingFloor.ini in WordPad and look for these lines:
TextureDetailInterface=Normal
TextureDetailTerrain=UltraHigh
TextureDetailWeaponSkin=UltraHigh
TextureDetailPlayerSkin=UltraHigh
TextureDetailWorld=UltraHigh
TextureDetailRenderMap=UltraHigh
TextureDetailLightmap=UltraHigh
Set them all to Normal.
Then start the game again and enter the setres command again if you need to apply the resolution again.
That should fix it if it is a problem with the resolution or the detail settings.
This should not happen though. The lowest resolution it should default to is 800x600 and the interface textures shouldn't go lower than Normal.
Driver forcing very low mipmap levels:
It could be that you are forcing a very low mipmap level for the textures through your graphics card driver. This would mean that you are forcing the use of very low-res versions of the textures, not dissimilar to turning the details down in-game except it's independent of that and is forced through the driver. Be sure to check this!
Zet suggested this already, but you didn't say if you tried it yet.
Graphics card is incompatible with D3D9 renderer:
It is also possible that your graphics card has a problem with the currently selected renderer. Open KillingFloor.ini in WordPad and change the following lines:
RenderDevice=D3D9Drv.D3D9RenderDevice
;RenderDevice=D3DDrv.D3DRenderDevice
;RenderDevice=Engine.NullRenderDevice
;RenderDevice=OpenGLDrv.OpenGLRenderDevice
;RenderDevice=PixoDrv.PixoRenderDevice
to
;RenderDevice=D3D9Drv.D3D9RenderDevice
RenderDevice=D3DDrv.D3DRenderDevice
;RenderDevice=Engine.NullRenderDevice
;RenderDevice=OpenGLDrv.OpenGLRenderDevice
;RenderDevice=PixoDrv.PixoRenderDevice
to change the renderer from D3D9 to D3D.
IF the pirated version works this is one helluva strange coincidence, btw. I know no one else who has this problem with the steam version of KF. Just so you know this isn't some widespread issue caused my some malicious DRM methods. Aside from the game requiring steam I don't think there even are any.
If anything it could be a problem with certain steam features, seeing that the pirated version probably runs without steam. Maybe disable the steam community chat overlay if nothing else helps. It's a long shot but who knows... It's caused problems before. Last resort though because this is just a wild stab in the dark.
Something mentioned above in bold should fix your problem.