Every Telegram image size
Telegram uses one square photo for people, channels and groups, a square for stickers, and a landscape shape that suits most post images.
Profile / channel photo
640 × 640 px, 1:1 Your DP, or a channel or group photo. Shown as a circle.
Post image
1280 × 720 px, 16:9 A landscape image for a channel post or chat.
Sticker
512 × 512 px, 1:1 Use a transparent background so the sticker looks cut out.
Channel photos that stand out in a chat list
In the chat list, your channel photo sits at a small size next to dozens of others. A bold symbol or initials on a plain colour is far easier to spot than a detailed photo.
If you run several channels for one brand, use the same style for each photo with one difference, such as the colour or a letter, so followers can tell them apart.
Stickers and post images
Stickers look best with a transparent background and a clear outline, because they are shown without a bubble behind them. Start from a PNG with transparency; the tool keeps it.
For channel posts, a landscape image with a short headline on it is read quickly as people scroll. Telegram lowers the quality of images sent as photos, so check how a text-heavy image looks after sending, and send it as a file if the text becomes hard to read.