You have heard of the saying GIGO (Garbage in Garbage out) Well this applies to engraving as well. If a logo or image looks blurry, then it is not suitable for engraving. Web images usually fall into this category.
For Glass and Acrylic engraving the ideal image should be good quality black and white (not greyscale) The preferred file type is the CorelDraw .cdr However as not many clients would use CorelDraw.
.eps or .ai are next best.
.jpg can often be suitable if resolution is high enough.
.pdf is usually just suitable for viewing an image or layout in original form.
and depending how it is saved, can be sometimes used.
.doc Word files sometimes work - sometimes not.
.pub Publisher files are not compatable - do not send these files
Some images may look great when small, but they may be low resolution and only a few kb (kilobytes) If you enlarge it and it shows the pixels, then it will not be suitable.
There are basically 2 types if images:
These are made up of pixels (square boxes) and are only able to be modified by a paint program. - examples .jpg. .tiff . gif
These are images made up of line drawings and are editable.
examples .eps .ai These are preferred