Howto question about gradual transparency

[Mariane]

Hi everyone,

I am trying to include a picture into an aquatic background. The picture is cut out and has a transparent background, the aquatic background is continuous (it fills up the whole picture rectangle). Both are in .png format but I will change this if you advise me to change it.

I would like to make the bottom part of the picture gradually fade out from 0% transparency to 100% transparency, so that when I paste it onto the background, the bottom part of the picture seems to be in the water.

I am used to kolourpaint and libreoffice draw. I tried to do it in gimp but I couldn't find how to do it.

Please tell me how to do this.

[Mariane]

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[Mariane]

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[shantiq]

this might help