Welcome to my first tutorial (probably not the last).
Thank You for wasting Your precious time at this short text. The main aim of this tutorial is to show You how to make some nice looking sigs with simple nature image with some effects and border. I'll guide You through brush settings and simple usage of PS filters. I hope it'll help You in some way...
Okay, enough talking. Let's do it.
My outcome:

1. Find some nice picture of any nature part You want (You can surely use any other image with car, human etc... but of course it won't be nature sig then.) I'm using this one: http://www.cdesign.nazwa.pl/tutorial/naturesig/orchidac.jpg
2. Create new document. Width: 350; Height: 125. Background doesn't matter. Set your image in the middle of screen like so:

3. Duplicate layer with Your image three times. I'm using default names of layers so I'll be using them also in this tut.
4. Select "Layer 1 copy". Then go Filter>Blur>Gaussian Blur. Set radius about 4~5 pixels. Set its Blending Mode to Overlay.
5. Select "Layer 1 copy 2". Go Filter>Artistic>Cutout (You can experiment with other filters but this one is the best for me). Aply this settings:

and set its Blending Mode to Saturation.
6. Select "Layer 1 copy 3". I deleted main "object" in image (as You can see at screen I used Rectangular Marque Tool with Feather set to 15).

Then I did the same as in step 4.
Okay. Now we should have something like that:

Do we? If not, try to refine it or just follow next steps with Your result.
7. Now we need to add some light effects. Create new layer. Grab Brush tool and use this settings:

Brush upper corners. Middle of brush should be out of our picture to make some glowing effect. Should look like this:

8. We're still using Brush Tool. Create new layer and use this settings

(Brush size beetwen 13 and 27). Brush to become effect like this:

Now You have to do something with this because it doesn't look good, does it? Again use Gaussian Blur filter with radius about 4 and set Blending Mode to Overlay. You can add some various to this ray using Smudge Tool. My result:

9. Now we're going to make some "dots streams". Grab Brush tool and set this settings:



Brush from the edges into the middle of image. My result:

10. Create new layer at the top of others and type ctrl+a to select all. Go Edit>Stroke. Width: 2 px; Color: #FFFFFF; Location: Inside. OK! And then set Blending Mode to Overlay. You can also add some text or something of course.
Once again my outcome:

And that's it! You're done! I hope this tutorial helped You in some way. You can try this in other projects.
Post Your outcomes or comments, will be welcomed.
Greetings








( Lowed the text opacity so it would blend better