Open up Gimp and go to >>>FILE>>>NEW>>>TEMPLATE and pick the>>>A4 SIZE;

209.97 Width,

297.01 Height

in mm. 

2480 Width

3508 Height

in px

Go to>>>IMAGE>>>GUIDES>>>NEW GUIDE BY PERECENT and pick>>>DIRECTION>>>HORIZONTAL>>>POSTION (In Percent)>>>50.00

And again Go to>>>IMAGE>>>GUIDES>>>NEW GUIDE BY PERECENT and pick>>>DIRECTION>>>VERTICAL>>>POSTION (In Percent)>>>50.00

Repeat this for how many photos you want and spread out the guides evenly over the page. I used eight boxes in total and I >>>HOVERED THE CURSOR over the guide and>>>HELD SHIFT  to drag around the guide into sections.

Using the>>>LASSO draw shapes and stick to the guide lines it should snap into place when you draw around the guides.

Go to>>>LAYER>>>TRANSPARENCY>>>ADD ALPHA CHANNEL. If it’s greyed out it’s been added and you can ignore this step. 

Once you have drawn a shape and it’s highlighted HOLD>>>CTRL>>>and>>>PRESS X to delete the background. If you have more than one layer you may want to swap layers and delete each layer’s background.

>>>OPEN UP first photo or >>>DRAG AND DROP into Gimp. Go to>>>LAYERS on the left hand side panel and put the first photo at the bottom of the layer. If you can’t see layers then go to>>>WINDOWS>>>DOCKABLE DIALOGS>>>LAYERS to get it to appear.

Now with the first photo layer selected use the>>>MOVE TOOL and>>>DRAG INTO POSITION  till it’s centred and visible in the transparent section.

Repeat Step 3, 5, 6 and 7 till you have your it filled out. You will have overlay on each section so remember to>>>DRAW AROUND EACH OVERLAYED BIT with the>>>LASSO and>>>HOLD>>>CTRL and>>>PRESS X to delete any unwanted bits. You must be selecting the right photo or it won’t delete.   

Selecting the>>>TOP LAYER on the left hand side panel go to>>>LAYER>>>ADD LAYER   

With the>>>TOP LAYER SELECTED  and using the>>>LASSO draw around the photos outline sticking to the outer of the photo and making them as even as possible but isn’t important.   

Repeat Steps 9 and 10  until it’s filled out.   

Selecting the top layer and the frames around your photos go to the>>>LAYERS SECTION on the left hand side  and>>>RIGHT CLICK ON TOP LAYER and press>>>MERGE DOWN. Do this for each bit of the frame keeping the photos separate. If you are unsure what is the frame then>>>PRESS THE EYE on the>>>LEFT HAND SIDE of the>>>LAYER SECTION for each bit of layer.

Use the>>>FUZZY SELECT TOOL and press any bit of the frame to highlight all the frame and leaving the photos unhighlighted. With the frame selected use>>>COLOURS>>>FILTERS>>> 

Export image by going to>>>FILE>>>EXPORT TO or>>>EXPORT AS and save with a  JPG or PNG extension EG; COLLAGE__INSERT NUMBER.jpg or COLLAGE__INSERT NUMBER.png.