Hey, that's pretty good start for a beginner. You didn't try to put 5 other transparent pictures on top of that. Thank god. Anyway, to answer your question, try a layer mask and gradient. I assume you are using photoshop. Go to the layer menu, add layer mask, hide all. Use the gradient tool, select the foreground to transparent preset and your foreground color as white. Then, apply the gradient to the layer mask.