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Look through the apps available in your app store and find one that interests you. Many of the photo collage apps are free to download and use, but they may have small pop up advertisements or include watermarks on your photos. Apps like PhotoGrid, PicStitch, and Pic Collage are free and available on iOS or Android. The app will ask to access your photos the first time you open it. Allow the app to look in your gallery so you can choose your photos. Pick images all of the same quality with similar subject matter so your collage looks cohesive. Pick as many photos as you want plus a few extra. You can always choose to remove them later. Drag and drop the photos into the layout of your choice. Some apps will provide specific layouts, but others will let you design your own. Adjust the borders and the image sizes to fit all of the photos you need into the collage. Change the border color to match your photos or see if there's an option to completely remove the borders. Some apps allow you to put filters on the individual images, while others will put a filter over the whole image. Try out a variety of filters to see which works best for the mood of your piece. If you want to add text or labels, look for a text option in the menu. Drag and drop the text where you want it and resize it so it fits into your collage. If your app doesn't let you apply filters, go into your phone's gallery and edit the image before putting it in your collage. Once you're happy with how your collage works, look for the save or export feature in the menu. Choose the highest quality and the size you need so you can save it to your phone's gallery. Some apps will allow you to post the collage directly to your social media accounts.
Download a photo collage app from your phone's app store. Select the photos to include in your collage. Edit the collage's layout and design. Add filters and text to your collage. Export the image to save it into your gallery.