You download a photo from a chat, crop it, and export it as JPEG again. The difference may seem small on a phone. Zoom into fine lines or a sky gradient and new artefacts may appear. A lossy export can discard more information each time a file is re-encoded along the editing chain.

Separate opening a file from encoding it again

Viewing a JPEG does not change the pixel data stored in the file. Exporting a new JPEG may run the image through an encoder again. Copying a file byte for byte does not recompress it. Check the output to see what a particular editor or sending mode actually did.

Look at three sensitive areas

At 100% zoom, compare hard edges, smooth gradients such as the sky, and fine textures such as hair or stone. Watch for halos near edges, blocks in shadows, and steps in gradients. Compare the copies at the same display size so scaling differences do not distort the result.

Keep the editing chain short

For the next revision, return to the original or a lossless working file. Apply the edit there and export the share format at the end. A higher quality setting cannot restore previously lost detail. If needed, reproduce the crop from the master.

Run a one-photo comparison

Export one copy from the master and another from a sharing JPEG at the same dimensions and settings. Compare file sizes and the three sensitive areas. Even if the difference is small, record which version should be used for another edit. Keep the master and final share copy in separate places.

Find the point at which detail was lost

Suppose a product photo goes from a phone to a computer, through an editor and finally into a team chat. When the tiny lettering on the product is hard to read in the last version, examine each step. The editor's export may still be sharp. Compare the dimensions and file size of the version downloaded from the chat. A change in dimensions means resizing is part of the difference. Equal dimensions can still hide a change in encoding quality. A blurry preview alone gives you little to go on. Open the downloaded copies in the same viewer at the same zoom. Look at the edges of lettering, the transitions in a plain background and the sharp outlines of the product. If the change appears after one step, keep its input and output together. Try making the final export directly from the master and compare it. This shows whether skipping an intermediate copy avoids another loss of detail. It also gives you an example you can share with the rest of the team.

Pick a size for each use

If a catalogue needs both a small listing thumbnail and a photo people will zoom into, use a different target for each. A small card may work even if you cannot see one fine line. On a product detail page, that line might distinguish a scratch from the pattern of the material. Make two exports from the master at different quality settings and review them at the size visitors will see. Choose the smallest copy that keeps the necessary information. Quality numbers can mean different things in different editors, so carry forward the result of your comparison as well as the setting. Use a demanding sample when judging the output. Hair, grass, small writing and a large open sky reveal different problems. Saving an already damaged copy at a higher quality cannot recover information that was lost. Return to the master and change the export there. Note the source of the delivery copy so that someone can repeat the process later. If you share the file with an editor, include the original location or label it as a delivery copy.