
Transparent areas turn white
Logos and icons with transparent backgrounds come out on solid white as JPGs. If you want to layer one over other designs, keep it as a PNG.

Is your PNG too big to attach, or does the site only take JPGs? You can convert it online: upload the file here and download it as a JPG. There's nothing to install.
You can select one static image file.
Converting files is free. You can select images between 32 and 8000px in both width and height.

Drag a PNG file onto the upload area, or click [Select PNG file] to choose one. Animated PNGs and files over 100 MB aren't supported.
Sign in before you click [Download JPG]. When you click it, the editor opens with your image on the canvas. If you sign in after the editor opens, your image won't carry over and you'll have to upload it again.
When the editor opens, a download panel appears with JPG already selected. Under [Size], 1x keeps your PNG's width and height, and 0.5x cuts both in half.
If all you need is the JPG, click [High resolution download] in that panel. To edit first, close the panel, make your changes, and reopen it with [Download] at the top right. This time the panel may show a different format, so pick JPG under [File format].

Photos and colorful screenshots are often much bigger as PNGs than as JPGs, which can push them over the size limit for an email attachment or a website upload.
Some sites won't accept anything but a JPG, no matter how small your file is. You'll often see this when adding a photo to an application or other online form. In that case, convert your PNG before you upload it.

Logos and icons with transparent backgrounds come out on solid white as JPGs. If you want to layer one over other designs, keep it as a PNG.

Saving as JPG costs a little quality. You'll rarely notice it in photos, but small text and thin lines can look fuzzy around the edges. If your PNG is over 23 MB, it's also compressed before it opens in the editor, which may lower quality a bit more.

Some images barely get smaller as JPGs. With simple graphics that use just a few colors, the PNG can even be the smaller file. If the JPG is still too big at 1x, reopen the panel with [Download] at the top right, pick JPG under [File format], and download it at 0.5x.
They differ mainly in file size, image quality, and transparency. For photos, a JPG is usually smaller than a PNG and looks nearly the same. Logos, icons, and text-heavy screenshots stay crisper as PNGs, and you'll need a PNG for a transparent background.
Yes. JPG and JPEG are two names for the same format, so just pick JPG under [File format].
For print, the image's size in pixels matters more than the file format. At the same dimensions, JPG is fine for photos, while PNG prints small text and thin lines a little sharper. To print your PNG as part of a multi-page document, try converting it to a PDF.