Telegram has provided everyone with a Photoshop Sticker Example file that can simplify the first steps to create your first set of stickers yourself!
To create sticker packs similar to those already published, the individual stickers must have a white stroke that outlines the image.
Download now the Sticker Example PSD file
Just open it on Photoshop and insert the image with transparent background and then export the file as .png.
Now that you have exported your .png sticker you need to Create a custom Telegram Sticker Pack