Fire up Inkscape.
►Choose the rectangles and Squares tool and make a narrow rectangle. Give it any color you like. I will make this one red.
►At the bottom of the page, and while the rectangle is selected, right-click on the Stroke and when the little menu appears, chose Edit Stroke and when the dialog box appears, click on the X, to take out the stroke.
►Now, go to Path, Object to Path. Click on the Nodes tool which is just below the Arrow or Select tool. When the nodes appear, click on one to select them, when you see that they turn blue, click on the center of the narrow rectangle and pull, while holding down the Shift key (that way the nodes will move symmetrically and your object will not be deformed.) Now you have a rounded corner.
►Duplicate what you have and drag the copy to one side. While it is selected, right-click on it so that the rotation arrows will appear and turn it around so that it will become the vertical portion of your photo corner.
Drag it to meet the other piece of the photo corner and join the so they match perfectly. Or, while it is selected, you can click on the 5th button from the left at the top of the page, to rotate selection 90 degrees. ►Then you need to join the two pieces, to avoid the appearance of a white line in between the two sections,
overlap the vertical portion of the photo corner over the horizontal just a bit. Adjust the size of your finished corner to your liking. I don't like my photo corners too long, but that is just a personal preference, you can make them anyway you like. When you like the way they look, elect everything with your mouse and go to Object, Group.
►To save, click on File, Export Bitmap to save as a PNG.
Because I want my corners for a wedding photo, I chose red (#ee0000) but you can choose any color you like or the one that goes best with your project.
Now let's decorate our corners using Gimp!
Fire up Gimp.
►Open your saved PNG in Gimp.
►Go to Filters, Noise, RGB Noise.
►Since my color is Red, I moved the Red lever to 0.70
While the Green and the Blue remained at 0.20
And the Alpha remained in 0.00
Then I clicked okay.
►Depending on your color, move the levers in the color you have chosen of the 3 Primary ones and allow a confetti or glitter effect to form. Click okay.
Let us make it a bit fancier. Choose the circle or ellipse tool. While holding down the Ctrl key, make a circle. Go to Layer, New Layer. Choose the Gradient tool
and from the Gradient tool menu choose the gradient Golden, leave it as a linear gradient. Make the gradient with your mouse vertically down the circle.
Go to Select, Shrink and shrink by 20 pixels. Go to Layer, Change the Foreground color to #fe0800 and the Background color to #a50000. Choose the Gradient tool and click on the color to change it to FG to BG (RGB) apply the Gradient.
►Go to Filters, Light and Shadow, Drop Shadow and apply a drop shadow of 15. Repeat the drop shadow as before, to give it more depth.
Chage the Foreground color to a yellow (I used #fefe00) choose the Brush tool and from the menu pick Circle Fuzzy (19), in the Toolbox menu, move the level of the Scale to 5.72 and the opacity to 30 percent. Click several times where you want the "shine" to be. After that, reapply a drop shadow with the same value as before to enhance the "shine."
►Go to Layer, Merge Down. Save as a PNG. If you want a drop shadow, (personally, I think it looks better with one) and you have downloaded the Free ScriptFu for your Gimp, go to ScriptFu and use their drop shadow, because for some reason, the Light and Shadow drop shadow from the Filters menu does not work after you have reached this point. If you don't have
the scriptfu downloaded get it and use it, if you prefer, take your corner back to Inkscape and duplicate it, make it black, give it a little blur and send it to the back of your corner. Select all and Group it and Export as a PNG. If you use scriptfu, give it a drop shadow or 12.
Then save as a PNG.
Now you can apply it to a photo like I did.