Basically the same as Johns technique, except with Smart Objects.
Create your document.
4 inches by 6 inches at 300ppi
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Go to LAYER > NEW FILL LAYER > SOLID COLOR
A color picker will appear
Make your color white (#ffffff)
Go to VIEW > NEW GUIDE
A menu will appear
Set the orientation to Vertical
Set the position to .250
Hit OK
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Go to VIEW > NEW GUIDE
A menu will appear
Set the orientation to Vertical
Set the position to 3.750
Hit OK
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Repeat this for the horizontal guides.
Your document should look like this....
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Next
Select your Rectangle Tool (not the Rectangular Marquis Tool)
In the Tools Option bar, Make sure shape is chosen, set your Fill Color to a grey, and make sure stroke is turned off.
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Click once on the document in the document window.
This will open a "Create Rectangle" menu
make your width 1.5in and your height 2in.
Place a check mark in the "From Center" selection.
This will create a rectangle shape layer!
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With the shape layer selected/highlighted, hit Cmd/Cntrl + J 3 times. This duplicates the shape layer.
Select your Move Tool and move the shapes to the corners or wherever you want them!
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Now rename all of the shape layers according to their positions.
Your layers panel should look like this...
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Choose any layer.
Right click in the body of the layer (not the thumbnail) and choose "Convert to Smart Object".
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Repeat this for the remaining 3 shape layers.
FINAL STEP
Now choose a SmartObject/Shape layer and double click the thumbnail.
This will open a PSB document in a new tab.
In the PSB doc,
Go to FILE > PLACE EMBEDDED
Select the baby image you wish to be in this rectangle (panel)
Use the control handles to resize the image to fit in the rectangle/panel.
When done, hit OK
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Close the PSB file and hit save!
Back in your original document you will now have the baby in that panel.
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Repeat the same "Final Step" for the remaining 3 rectangle/panels.
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Your final layers panel will look like this......
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Everything is editable.
The background color can be changed.
The rectangles can be resized and moved to different positions.
If you want to change a baby's photo, just repeat the "Final Step" for each.
Here, I have repositioned the panels and changed the BG color.
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