In Photoshop open a new file at 300 dpi the size you want to print your poster. In this case I've started with a 10"x14".
Place the images you wish to use in the layout in a separate folder. Depending on how many images you wish to use, determine the dimensions you will need to make each image. Keep the dpi at 300, the same as the new file layout.
This point is arbitrary, you may want to size 1 or 2 images and place them in the layout to see how the sizing looks from your artistic point of view. Each image can be cropped using the crop tool set to your chosen dimensions and
300 dpi. Once you have decided the size and correct number of images, move the images onto the layout file.
Make sure auto select layer is checked in the options bar so you can freely select and move images in your layout. Use the checker board pattern to line up the images with the desired spacing. Use the arrow keys on a selected image or layer to move it up and down or right and left to fine tune the image placement.
Once you are satisfied with the layout go to the layers palette, highlight layer #1 and fill that layer with the color you wish to use as the background color. Go to edit> fill choose foreground > opacity 100%> ok.
In the finished image I have added the title.
If you prefer a very thin line and a bleed on the edges you can use the paint brush to make the lines.
Start by butting all of the images side by side and top to bottom. Again leave an area for the title text.
Go to the paint brush in the tool box. In the options bar make the brush hard by holding the shift key and tapping the right bracket key. Make the brush as small as desired for the size line you wish to make. Set the mode to normal > opacity to 100%. Place the brush to the left, where the top images join top to bottom, and click once, then move the brush to the right side exactly where the images join. Hold the shift key and left click. A straight line will connect the two points. Line all of the areas where the images join each other. Fill the title area and type in the title.
Obviously any layout can work for a poster. The only limitations are your image size and your imagination.
