Canon EOS REBEL T7i Instruction Manual page 441

The image is out of focus or blurred.
Set the lens's focus mode switch to <AF> (p.49).

Press the shutter button gently to prevent camera shake (p.51-52).

If the lens has an Image Stabilizer, set the IS switch to <1>.

In low light, the shutter speed may become slow. Use a faster shutter

speed (p.186), set a higher ISO speed (p.152), use flash (p.204), or
use a tripod.
There are fewer AF points.
Depending on the attached lens, the number of usable AF points and

patterns varies. The lenses are categorized into eight groups from A to
H. Check which group your lens belongs to. Using a lens in Groups E
to H will have fewer usable AF points (p.133-134).
The AF point is blinking.
Regarding the AF points lighting up or blinking when you press the

<S> or <B> button, see page 126.
The AF points do not light up in red.
The AF points light up in red only when focus is achieved in low light or

with a dark subject.
In Creative Zone modes, you can set whether to have the AF points

light in red for when focus is achieved (p.394).
Troubleshooting Guide
441