Image optimization: a practical guide

It is rarely the thing that gets a project approved, and often the thing that decides how it goes. This guide covers what image optimization actually involves, where it usually goes wrong, and how to tell whether yours is in reasonable shape.

Real-world numbers from actual visitors matter more than a score produced on a fast laptop. Nothing below assumes a large team or a large budget — most of it is a decision somebody has to make and then write down.

Why this earns attention

Images are usually the largest thing on a page. There is a version of this that is over-engineered, and it is worth avoiding. Doing this properly once is usually cheaper than doing it approximately three times.

For most businesses the question is not whether this matters but how much of it is worth doing right now. That depends on what you are trying to achieve in the next few months, not on best practice in the abstract. There is a version of this that is over-engineered, and it is worth avoiding.

The practical version

Modern formats cut file size substantially at the same quality. Getting it slightly wrong is survivable. Ignoring it entirely is not. The version that survives contact with a real deadline is the simple one.

Speed is a feature people notice only in its absence, and then they leave rather than complain. The version that works in practice is usually less elaborate than the version described in the guides.

Serving a 3000px image into a 400px slot is pure waste. None of that requires a large budget, only a decision and someone to own it. Assume whoever inherits this will have half your context and none of your patience.

A working checklist

If you want a quick read on where you stand, work through this. Anything you cannot answer confidently is where to start.

• Images are usually the largest thing on a page
• Modern formats cut file size substantially at the same quality
• Serving a 3000px image into a 400px slot is pure waste
• Someone is named as the owner, not just assumed to be
• There is a date in the calendar to review it again
• The decision and the reasoning behind it are written down somewhere findable
• You could explain the current setup to a new hire in five minutes

The mistakes we see most

The most common failure is not doing this badly. It is doing it once, during a launch, and never revisiting it. Circumstances move, the setup does not, and the gap widens quietly until something breaks or somebody notices the numbers.

• It was configured during a launch and has not been touched since
• Different people in the business believe different things are true about it
• There is no way to tell whether the last change helped or hurt
• The only person who understands it has left, or is about to

Performance work is mostly subtraction, which makes it unpopular and effective. Small and consistent beats large and occasional here.

How we approach it

On our projects this gets handled during the build rather than added afterwards, because retrofitting it costs several times more than including it. We write down what was decided and why, so the next person to touch it is not guessing.

If you are working with someone else, the questions worth asking are simple: who owns this, how will we know it is working, and what happens when it needs to change?

Turning this into a decision

Pick the single item from the checklist above that would cause the most trouble if it turned out to be wrong. Fix that one, confirm it worked, then move on. Most of the value here comes from doing the first two things, not all of them.