Yes you can

. You have to copy the logo you want to use as an overlay into a layer.
It goes as follows :
1) Open your photo in Gimp;
2) Open your logo in Gimp;
3) Hit Ctrl+A on your logo to select everything;
4) Hit Ctrl+C to copy your logo;
5) Go on your photo and hit Ctrl-V to paste the logo. Gimp then makes a "Flotting selection" which is a copied layer. Hit the "New layer" button in the layer window to apply the import.
6) If you want, you can then change the layer mode or the opacity to give it a transparent effect.
Hope that helps

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