This is a re-write from the original that I forgot to save...oops...so bear with me lol.
The image used is of a friend of mine, Stacey (StungByFate).
I'm using GIMP 2.8 in case you're wondering, and I haven't really used it for awhile so I'm just going to show you the animation and leave the fancy bits like adding textures and text to you guys lol. The animation can look good either above or below the text, really just your preference/how it looks with your styling.
Open your image and crop/size down so it's 100x100.
You should just have your base layer of the image.
You're going to duplicate this layer so you have 4 of it. From top to bottom, name them: "Top Right Corner"
"Bottom Left Corner"
Turn the visibility off for the Top Right Corner and the Middle layers for now. This is just to make sure we can see what we're doing with the shine layer.
Step Two: Shine Layer for the Bottom Left Corner
Using your pencil tool, set the brush to Block 01, size 200, angle 45.
Add a transparent layer above the Bottom Left Corner layer. This is the layer you will add the shine to. Add it so it covers the bottom left corner like in the picture below:
Step Three: Shine Layer for the Middle Layer
Add a new transparent layer above the Middle Layer. On this new layer, using your pencil tool again, make another block right next to the first one you did. You can move the layer if you have any gaps/overlaps to adjust it so there are none.
Step Four: Shine Layer for the Top Right Corner Layer
Add another transparent layer, this time above the Top Right Corner layer. Take your pencil tool again and make the last block right next to the middle one. Move the layer to adjust placement if needed.
Step Five: Blur the Shine Layers
Go to the first shine layer you made. Go to Filters > Blur > Gaussian Blur with a Blur Radius of 40px.
Do this for all 3 of your shine layers.
Then change the opacity of all 3 Blur layers to 25%.
Step Six: Merge Layers
Now with a total of 7 layers, we're going to need to merge some of them. Turn your 2 layers visibility back on.
Merge the layers down like so: Layer onto Bottom left corner
Layer #1 onto Middle
Layer #2 onto top right corner
You should now have 4 layers:
You're going to need to duplicate each one of them so they're like this:
Then you should be able to File > Export, make sure to save it as a GIF. To do this you can name it like
Click export > make sure "As Animation" is checked > Loop Forever > Export
This animation can sometimes make your graphics in larger KB sizes, so it isn't always recommended to do it in GIMP. Photoshop can make the file size smaller or you can use a GIF reducer.