The following table shows the effect of all available formats.
Description
You type
You getmonsssssssssssssssssssssssteerrrrrrrrrrrrmaagagaga
no format specified
Rendered as a floating block: no
Rendered inline: yes
Rendered caption: no
... text text text
[[File:example.jpg|caption]]
text text text ...
I am a monsssssssssssssssssssssssteerrrrrrrrrrrrmaagagaga
border results in a very small gray border
Rendered as a floating block: no
Rendered inline: yes
Rendered caption: no
... text text text
text text text ...
... text text text
text text text ...
frameless, like thumbnail, respect user preferences for image width, but without border and no right float
Rendered as a floating block: no
Rendered inline: yes
Rendered caption: no
... text text text
text text text ...
... text text text
text text text ...
frameless and border
Rendered as a floating block: no
Rendered inline: yes
Rendered caption: no
... text text text
text text text ...
... text text text
text text text ...
frame
Rendered as a floating block: yes
Rendered inline: no
Rendered caption: yes
... text text text
text text text ...
... text text text
text text text ...
thumb or thumbnail
Rendered as a floating block: yes
Rendered inline: no
Rendered caption: yes
... text text text
text text text ...
... text text text
text text text ...
When the height of an image in thumbnail is bigger than its width (i.e. in portrait orientation rather than landscape) and you find it too large, you may try the option upright=N, where N is the image's aspect ratio (its width divided by its height, defaulting to 0.75). The alternative is to specify the desired maximum height (in pixels) explicitly.
Note that by writing thumb={filename}, you can use a different image for the thumbnail.