Grouped in the order that turns what you shot into something you can publish: a format that opens, a weight that loads, colour you can check, several images as one, and a way for people to arrive.
HEIC, what an iPhone shoots by default, is a good format — the same quality at roughly half the weight of a JPG. The problem is the other end: older Windows machines, government upload forms and some editors still cannot open it.
So converting to JPG before you send anything is the real first step. If you are worried about quality, the order matters: convert HEIC to JPG once, then do all your resizing and compressing on that JPG. Every conversion re-encodes the image, and the losses stack.
If you need transparency, the target is PNG rather than JPG. Turning a logo or a cut-out subject into a JPG fills the empty area with white.
The goal for an image on the web is not «as good as possible», it is «only as much as needed». A single 3MB photo in the body of a page slows it down on mobile, and slow pages rank worse as well as feeling worse.
Fixed targets save you from deciding every time. Body images at 1,200 to 1,600px wide and around 200KB; thumbnails in the 400px range under 50KB. Unless you are printing, anything past that is usually waste.
And resize before you compress. Dropping the quality on a 4,000px image leaves it both heavy and mushy; shrinking it to 1,600px first and then compressing gives you a far cleaner picture at the same file size.
Palettes that look good on screen frequently fail to be readable. Pale grey text on a grey background is fine on a designer's large monitor and invisible on a phone outdoors.
So read the contrast ratio alongside the colour. Body text needs at least 4.5:1 against its background and large headings at least 3:1. That is a measurement rather than a preference, which is exactly why it should not be judged by eye.
Moving between notations is constant too. Design tools speak HEX, modern CSS increasingly speaks OKLCH, and the shared document has RGB in it. Converting the same colour three ways is not work worth doing by hand.
When building a palette from nothing, deriving it from one colour is safer than picking each by feel. A complement gives you one accent, analogous colours give you layers of the same family, and a triad gives three colours with distinct jobs — in each case the relationship is explicit.
A GIF is the answer when you need to show motion and a video would be too much. What changes when a button is pressed, how a three-step process flows — it autoplays, it is silent, and it drops into documentation without a player.
The cost is weight. GIF is an old format that stores at most 256 colours per frame, so real footage balloons to several megabytes fast. Cutting the frame count and the width first is the only way to lose weight without losing what the animation was showing.
Fixed-spec photos are a different job again. Passports, visas and job applications each dictate the head height and the margins, so the aim is not a flattering crop but a compliant one.
A QR code is the one reliable way to move somebody from outside a screen to inside one. Posters, business cards, exhibition panels, a slide at the end of a talk — ask people to type a URL and most of them will not.
If it is going on paper, give it room. Around 2cm per side is the practical floor in print, and the code needs a quiet margin around it to be read at all. Butting it up against artwork is a common reason a code refuses to scan.
Keep the encoded URL short. Long tracking parameters make the grid denser, and a denser grid is far more sensitive to print quality and to the angle somebody points a camera at it.
It does not edit for you. These tools crop, shrink, convert and measure; none of them retouches.
And nothing is uploaded. Conversion, compression and GIF assembly all run inside the browser, which is a practical difference if you handle other people's photographs or unreleased material. With no upload, large files are also not limited by your connection.
The trade is browser memory. Feeding in many very large files at once can make the tab struggle, and working through them in batches is usually faster than pushing everything through at one go.